clk: sunxi-ng: Add sun5i CCU driver

The Allwinner A10s, A13, R8 and NextThing GR8 are all based on the same
silicon, and all share the same clocks.

However, they're not packaged in the same way, and therefore not all the
controllers are actually available on all these SoCs.

Introduce a clock controller driver for all these SoCs with different
compatibles to take that into account.

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