arm64: dts: allwinner: h6: move MMC pinctrl to dtsi

There is only one pinmuxing available for each MMC controller.

Move the pinctrl to the SOC

Signed-off-by: Clément Péron <peron.clem@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>