led: leds-qpnp-flash: change flash LED enablement method

Current flash LED enablement method glows LEDs one after another.
When it comes with battery current limit, two consecutive battery
level query causes inaccurate reading and delay in enablement,
which is not tolerable to camera and PMIC. In order to overcome
this issue, a new node is introduced as a switch, to provide
capability to glow both LEDs together. This addresses these
issues.

CRs-Fixed: 793302
Change-Id: I7e1689cc521f145bcfa3519c6f21e93d907f3408
Signed-off-by: Jigarkumar Kishorkumar Zala <j_zala@codeaurora.org>