ARM: sun8i: Introduce A23 Evaluation Board Support

The A23 Evaluation Board has an MMC slot, two UARTs, NAND, a few display
connectors (RGB, MIPI, LVDS), a mini-PCIE slot, USB host and OTG and a
bunch of embedded sensors.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>