sunxi: remove CONFIG_MMC?_CD_PIN

sunxi: remove CONFIG_MMC?_CD_PIN

For legacy reasons we were defining the card detect GPIO for all sunxi
boards in each board's defconfig.
There is actually no need for a card-detect check in the SPL code (which
consequently has been removed already), and also in U-Boot proper we
have DM code to query the CD GPIO name from the device tree.

That means we don't have any user of that information left, so can
remove the definitions from the defconfigs.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>
Tested-by: Samuel Holland <samuel@sholland.org>