dt-bindings: i2c: sun6i-p2wi: Add YAML schemas

Switch the DT binding to a YAML schema to enable the DT validation.

Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>