regulator: add bcm590xx regulator driver

Add a regulator driver for the BCM590xx PMU voltage regulators.
The driver supports LDOs and DCDCs in normal mode only. There is
no support for low-power mode or power sequencing.

Signed-off-by: Matt Porter <mporter@linaro.org>
Reviewed-by: Tim Kryger <tim.kryger@linaro.org>
Reviewed-by: Markus Mayer <markus.mayer@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>