regulator: bd70528: Support ROHM BD70528 regulator block

BD70528MWV is an ultra-low Iq general purpose single-chip power
management IC for battery-powered portable devices.

Add support for controlling 3 bucks and 3 LDOs present in
ROHM BD70528.

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