ARM: dts: sun6i: Add A31 Hummingbird support

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
[wens@csie.org: enable usbphy, ehci0, ohci0 for on-board usb hub, i2c0]
[wens@csie.org: drop uart2 (BT chip has no power), uart3 (no device)]
Signed-off-by: Chen-Yu Tsai <wens@csie.org>