mediatek: mt7622: build AHCI driver as module

Build the driver for the in-SoC AHCI SATA host as module, just like for
the other subtargets. No board requires booting off SATA, so we don't
need to have it built-in. All boards with SATA support already select
kmod-ata-ahci-mtk which provides the module.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/mediatek/mt7622/config-5.10

@@ -1,5 +1,4 @@
 CONFIG_64BIT=y
-CONFIG_AHCI_MTK=y
 CONFIG_ARCH_DMA_ADDR_T_64BIT=y
 CONFIG_ARCH_KEEP_MEMBLOCK=y
 CONFIG_ARCH_MEDIATEK=y