ARM: dts: sun8i: a83t: Move mmc1 pinctrl setting to dtsi file

mmc1 only has 1 possible pinmux setting.

Move any settings to the dtsi file and set it by default.

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