leds: leds-qpnp-flash: add PON regulator support

Add PON regulator support to torch LED, in order to set the spare
register bits of PON peripheral to avoid torch blinking in suspend.
Flash LED enables PON regulator when torch LED is in use, in order
to set the spare bits, and disables regulator when torch LED is
disabled.

Change-Id: I01901bec013047963fc72ec1928f0aceaac00e86
Signed-off-by: Jigarkumar Kishorkumar Zala <j_zala@codeaurora.org>