dt-bindings: regulator: Document ROHM BD71282 regulator bindings

Document ROHM BD71828 PMIC regulator device tree bindings.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Link: https://lore.kernel.org/r/0985fec1cce98b1db66e5df2d9bcf2dfd9c224a7.1576054779.git.matti.vaittinen@fi.rohmeurope.com


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