uboot-imx

sunxi: Enable CMD_GPT by default

GPT is pretty common these days and can be useful for things like fastboot.
Add a platform imply, so that users can still opt out if they wish so.

Reviewed-by: Jagan Teki <jagan@openedev.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>