ARM: dts: sun4i: Add pin-muxing info for the mmc0 controller

mmc0 is the only controller actually being used on boards, so limit the
pin-muxing options to that.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>