Regulator: Add TPS6507x regulator driver

Adding support for TI TPS6507x regulator driver

Signed-off-by: Anuj Aggarwal <anuj.aggarwal@ti.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>