sunxi: clk: A80: add MMC clock support

The A80 handles resets and clock gates for the MMC devices differently,
outside of the CCU IP block. Consequently we have a separate clock
device with a separate binding for that.

Implement that with the respective clock gates and resets to allow the
A80 taking part in the DM_MMC game.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
[jagan: fix a80 mmc clock config compatible]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>