arm64: allwinner: h5: add support for NanoPi NEO2 board

NanoPi NEO2 is a board with the same size factor with the original
NanoPi NEO by FriendlyELEC.

It has a H5 instead of H3 on NanoPi NEO, and the ethernet is upgraded to
1Gbps (with external RTL8211E PHY).

Add support for this board.

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