ARM: gr8: Add CHIP Pro support

The CHIP Pro is a small embeddable board. It features a GR8, an AXP209
PMIC, a 512MB SLC NAND and a WiFi/BT chip.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>