octeontx: add FAT FS support to kernel

The CN80XX Boot firmware uses an embedded FAT12 filesystem. For some reason
busybox can't mount this unless its enabled static in the kernel.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>

target/linux/octeontx/config-4.14

@@ -235,6 +235,7 @@ CONFIG_F2FS_STAT_FS=y
 CONFIG_FAIR_GROUP_SCHED=y
 CONFIG_FANOTIFY=y
 CONFIG_FANOTIFY_ACCESS_PERMISSIONS=y
+CONFIG_FAT_FS=y
 CONFIG_FIXED_PHY=y
 CONFIG_FIX_EARLYCON_MEM=y
 CONFIG_FRAME_POINTER=y
@@ -396,6 +397,7 @@ CONFIG_MMC_BLOCK=y
 CONFIG_MMC_CAVIUM_THUNDERX=y
 # CONFIG_MMC_TIFM_SD is not set
 CONFIG_MODULES_USE_ELF_RELA=y
+CONFIG_MSDOS_FS=y
 # CONFIG_MTD is not set
 CONFIG_MUTEX_SPIN_ON_OWNER=y
 CONFIG_NEED_DMA_MAP_STATE=y