regulator: add new regulator driver for lp872x

This driver supports TI/National LP8720, LP8725 PMIC.

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Reviewed-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>