regulator: bindings: ROHM bd70528 regulator bindings

ROHM bd70528 is a ultra low power PMIC which includes
3 bucks, 3 LDOs and 2 LED drivers. Document the bindings
for them.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Mark Brown <broonie@kernel.org>