Add the binding document for Richtek RT6245.

Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1622699844-19203-1-git-send-email-u0084500@gmail.com


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