ARM: dts: sun6i: Add pinmux settings for mmc1 to dtsi

mmc1 is used to connect to the WiFi chip on the Hummingbird A31.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
[maxime: Changed the drive and pull values for their defines]
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>