configs: Migrate and re-enabled CONFIG_CMD_MTDPARTS

Now that CMD_UBI does not select CMD_MTDPARTS we need to make platforms
that had been enabling it turn it on by hand.  This exposed that we had
not yet migrated CMD_MTDPARTS fully, so do so now.

Fixes: 86dfa556 ("cmd: ubi: Remove useless call to mtdparts_init()")
Signed-off-by: Tom Rini <trini@konsulko.com>