dt-bindings: timer: Convert Allwinner A13 HSTimer to a schema

dt-bindings: timer: Convert Allwinner A13 HSTimer to a schema

The newer Allwinner SoCs have a High Speed Timer 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>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>