Kconfig: Migrate FS_FAT / FAT_WRITE

Now that these symbols are in Kconfig, migrate all users.  Use imply on
a number of platforms that default to having this enabled.  As part of
this we must migrate some straglers for CMD_FAT and DOS_PARTITION.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/kzm9g_defconfig b/configs/kzm9g_defconfig
index bc3e5d9..a884e5a 100644
--- a/configs/kzm9g_defconfig
+++ b/configs/kzm9g_defconfig
@@ -13,4 +13,5 @@
 CONFIG_CMD_FAT=y
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y
+# CONFIG_FAT_WRITE is not set
 CONFIG_OF_LIBFDT=y