ARM: dts: sun9i: Add mmc1 pinmux setting

On the A80, mmc1 is available on pingroup G. Designs mostly use this
to connect to an SDIO WiFi chip.

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