sunxi: add support for Pine H64 board

Pine H64 is a SBC with Allwinner H6 SoC produced by Pine64. It features
1GiB/2GiB/4GiB(3GiB usable) DRAM, two USB 2.0 ports, one USB 3.0 port
and a mPCIE slot.

Add support for it.

The device tree is from Linux next-20180720.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com>