ARM: sun8i: v3s: add pinmux for mmc1

The dock board of Lichee Pi Zero features a MicroSD slot on MMC1, which
can be used with a MicroSD card or the MicroSD-slot Wi-Fi card provided
by Lichee Pi Zero.

Add pinmux for the mmc1 controller, and specify it in the mmc1 device
node as it's the only pinmux for mmc1.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>