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/r8a7795_salvator-x_defconfig b/configs/r8a7795_salvator-x_defconfig
index 60e0b72..1eba299 100644
--- a/configs/r8a7795_salvator-x_defconfig
+++ b/configs/r8a7795_salvator-x_defconfig
@@ -16,6 +16,7 @@
 CONFIG_CMD_NFS=y
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y
+CONFIG_CMD_FAT=y
 CONFIG_CMD_DHCP=y
 CONFIG_CMD_USB=y
 CONFIG_USB=y