regulator: tps65132-regulator: add driver for TPS65132 regulator chip

TPS65132 is a dual output regulator chip. It is usually used for
providing positive and negative supply voltages for LCD panel source
driver ICs.

The chip has a positive supply rail and a negative supply rail. Both
rails support 4V~6V output voltage range and each rail can be
controlled separately.

Change-Id: I6012bc8dd0f19a8cd6a94fe00457fc65b8408346
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>