dt-bindings: regulator: mt6360: Add DT binding documentation

Add a devicetree binding documentation for the mt6360 regulator driver.

Signed-off-by: Gene Chen <gene_chen@richtek.com>
Link: https://lore.kernel.org/r/1598438958-26802-3-git-send-email-gene.chen.richtek@gmail.com


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