imx7dsabresd: Fix the boot of a NXP kernel

Booting a NXP kernel with mainline U-boot leads to the following
kernel crash:

,----
| caam: probe of 30900000.caam failed with error -11
| Unable to handle kernel NULL pointer dereference at virtual address 00000004
| pgd = 80004000
| [00000004] *pgd=00000000
| Internal error: Oops: 805 [#1] PREEMPT SMP ARM
`----

This happens because NXP kernel expects MX7 to boot in secure mode,
so introduce mx7dsabresd_secure_defconfig that selects CONFIG_MX7_SEC
and allows booting a NXP provided kernel successfully.

Change-Id: Ic05912c1328c75e8e25c89e7543b67c8c214e20d
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>

conf/machine/imx7dsabresd.conf

@@ -18,7 +18,7 @@ KERNEL_DEVICETREE = "imx7d-sdb.dtb imx7d-sdb-epdc.dtb imx7d-sdb-gpmi-weim.dtb \
                      imx7d-sdb-reva-touch.dtb imx7d-sdb-reva-wm8960.dtb"
 
 UBOOT_CONFIG ??= "sd"
-UBOOT_CONFIG[sd] = "mx7dsabresd_config,sdcard"
+UBOOT_CONFIG[sd] = "mx7dsabresd_secure_config,sdcard"
 UBOOT_CONFIG[qspi1] = "mx7dsabresd_qspi1_config"
 UBOOT_CONFIG[nand] = "mx7dsabresd_nand_config,ubifs"
 UBOOT_CONFIG[epdc] = "mx7dsabresd_epdc_config"