ARM: dts: sunxi: h3-h5: Move pinctrl of mmc0 from dts to dtsi

Most of the boards use the mmc0 pins and their attributes defined in
mmc0_pins_a. Let's default to those by moving the pinctrl attributes
to the dtsi file. This makes it easier to modify device trees in the
future as there is only one place to change the pinctrl attributes.

Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>