leds: qti-flash: Add support for bharger flash

PM2250 flash is driven by the charger in reverse boost
(bharger) mode instead of the BoB regulator. Add the
necessary changes to support the same.

Change-Id: I04f9b5a3e4eb2f0e005dec1a1aec0294ddf24bb0
Signed-off-by: Kavya Nunna <knunna@codeaurora.org>