dt-bindings: clk: Convert Allwinner CCU to a schema

The Allwinner SoCs have a clocks controller supported in Linux, with a
matching Device Tree binding.

Now that we have the DT validation in place, let's convert the device tree
bindings for that controller over to a YAML schemas.

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