ARM: sunxi: Support the Nextthing GR8

The GR8 is an SoC made by Nextthing Co, loosely based on the sun5i family.

It has a number of new controllers compared to the A10s and A13 (SPDIF, I2S),
but some controllers missing too (Ethernet, less I2C, less UARTs).

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