ARM: dts: sun8i: Add pin-muxing info for the mmc controllers

This adds pin-muxing info for the mmc controller / port combinations
which are known to be used on actual boards.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>