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/novena_defconfig b/configs/novena_defconfig
index 49b963c..3c7589b 100644
--- a/configs/novena_defconfig
+++ b/configs/novena_defconfig
@@ -39,4 +39,5 @@
 CONFIG_USB_GADGET=y
 CONFIG_CI_UDC=y
 # CONFIG_VIDEO_SW_CURSOR is not set
+CONFIG_FAT_WRITE=y
 CONFIG_OF_LIBFDT=y