ramips: use parser_trx for Buffalo WCR-1166DS

Buffalo WCR-1166DS uses trx-fomatted firmware and the custom magic
number (0x5C436F74, "\Cot") is required for OpenWrt installation from
OEM WebUI.
But the current mtdsplit_trx doesn't support the custom magic number and
fail to parse and split to kernel and rootfs when the factory image is
flashed. Then, the kernel fails to mount rootfs automatically and panics.

Before the commit fddc78b, mtdsplit_trx
was patched in ramips target and the device-specific magic number was
supported only for WCR-1166DS[1].
But the patch was not inherited to the later version of the kernel and
deleted by the above commit, then, the custom magic number support was
broken.

[1]: https://github.com/openwrt/openwrt/blob/05d6e92594c507dcd1f4be6c1bcb2282fe1abe1f/target/linux/ramips/patches-4.4/0400-mtd-mtdsplit-add-support-for-custom-trx-magic-for-Buffalo-WCR-1166DS.patch#L27

log (factory image):

[    1.165312] spi-mt7621 10000b00.spi: sys_freq: 193333333
[    1.195782] spi-nor spi0.0: w25q128 (16384 Kbytes)
[    1.205353] 7 fixed-partitions partitions found on MTD device spi0.0
[    1.217938] Creating 7 MTD partitions on "spi0.0":
[    1.227436] 0x000000000000-0x000000030000 : "u-boot"
[    1.238427] 0x000000030000-0x000000040000 : "u-boot-env"
[    1.250123] 0x000000040000-0x000000050000 : "factory"
[    1.261306] 0x000000050000-0x000000810000 : "firmware"
[    1.282051] 0x000000810000-0x000000fd0000 : "firmware2"
[    1.293594] 0x000000fd0000-0x000000fe0000 : "glbcfg"
[    1.304719] 0x000000fe0000-0x000000ff0000 : "board_data"
...
[    1.452424] /dev/root: Can't open blockdev
[    1.460619] VFS: Cannot open root device "(null)" or unknown-block(0,0): error -6
[    1.475434] Please append a correct "root=" boot option; here are the available partitions:
[    1.491986] 1f00             192 mtdblock0
[    1.491989]  (driver?)
[    1.504938] 1f01              64 mtdblock1
[    1.504941]  (driver?)
[    1.517885] 1f02              64 mtdblock2
[    1.517888]  (driver?)
[    1.530831] 1f03            7936 mtdblock3
[    1.530834]  (driver?)
[    1.543777] 1f04            7936 mtdblock4
[    1.543781]  (driver?)
[    1.556724] 1f05              64 mtdblock5
[    1.556727]  (driver?)
[    1.569672] 1f06              64 mtdblock6
[    1.569675]  (driver?)
[    1.582617] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[    1.598976] Rebooting in 1 seconds..

This patch fixes this issue by using parser_trx with specifying custom
magic number in dts instead of mtdsplit_trx.

log (fixed factory image):

[    1.202044] spi-mt7621 10000b00.spi: sys_freq: 193333333
[    1.225369] spi-nor spi0.0: w25q128 (16384 Kbytes)
[    1.235015] 7 fixed-partitions partitions found on MTD device spi0.0
[    1.247603] Creating 7 MTD partitions on "spi0.0":
[    1.257106] 0x000000000000-0x000000030000 : "u-boot"
[    1.269447] 0x000000030000-0x000000040000 : "u-boot-env"
[    1.281192] 0x000000040000-0x000000050000 : "factory"
[    1.294208] 0x000000050000-0x000000810000 : "firmware"
[    1.305774] 2 trx partitions found on MTD device firmware
[    1.316540] Creating 2 MTD partitions on "firmware":
[    1.326399] 0x00000000001c-0x000000214754 : "linux"
[    1.336063] mtd: partition "linux" doesn't start on an erase/write block boundary -- force read-only
[    1.357070] 0x000000214754-0x0000007c0000 : "rootfs"
[    1.366994] mtd: partition "rootfs" doesn't start on an erase/write block boundary -- force read-only
[    1.386368] mtd: device 5 (rootfs) set to be root filesystem
[    1.398700] 1 squashfs-split partitions found on MTD device rootfs
[    1.411027] 0x000000520000-0x0000007c0000 : "rootfs_data"
[    1.422841] 0x000000810000-0x000000fd0000 : "firmware2"
[    1.436282] 0x000000fd0000-0x000000fe0000 : "glbcfg"
[    1.447408] 0x000000fe0000-0x000000ff0000 : "board_data"
...
[    1.611216] VFS: Mounted root (squashfs filesystem) readonly on device 31:5.

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>

target/linux/ramips/dts/mt7628an_buffalo_wcr-1166ds.dts

@@ -146,7 +146,8 @@
 			};
 
 			partition@50000 {
-				compatible = "openwrt,trx";
+				compatible = "brcm,trx";
+				brcm,trx-magic = <0x746f435c>;
 				label = "firmware";
 				reg = <0x50000 0x7c0000>;
 			};

target/linux/ramips/image/mt76x8.mk

@@ -68,7 +68,7 @@ define Device/buffalo_wcr-1166ds
   BUFFALO_TAG_VERSION := 9.99
   BUFFALO_TAG_MINOR := 9.99
   IMAGES += factory.bin
-  IMAGE/sysupgrade.bin := trx | pad-rootfs | append-metadata
+  IMAGE/sysupgrade.bin := trx -M 0x746f435c | pad-rootfs | append-metadata
   IMAGE/factory.bin := trx -M 0x746f435c | pad-rootfs | append-metadata | \
 	buffalo-enc WCR-1166DS $$(BUFFALO_TAG_VERSION) -l | \
 	buffalo-tag-dhp WCR-1166DS JP JP | buffalo-enc-tag -l | buffalo-dhp-image