regulator: dt-bindings: Add Richtek RT4803

Add the binding document for Richtek RT4803.

Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/1680050606-461-1-git-send-email-cy_huang@richtek.com


Signed-off-by: Mark Brown <broonie@kernel.org>