dt-bindings: clocks: Convert Allwinner A80 DE clocks to a schema

The Allwinner A80 SoC has a display clocks controller that is 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.

Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>