regulator: tps80031: add regulator driver for tps80031

Add regulator driver for Texas Instrument TPS80031/TPS80032 device.
TPS80031/ TPS80032 Fully Integrated Power Management with Power
Path and Battery Charger. It has 5 configurable step-down
converters, 11 general purpose LDOs, VBUS generator and digital
output to control regulators.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>