dt-bindings: leds: Add DT bindings for qpnp-flash-v2

Add DT bindings for QPNP Flash LED v2 driver that supports camera
flash operation.

This is taken as a snapshot from msm-4.14 kernel
'commit 9bb584ae ("msm/sde/rotator: Add rev checks for sdmmagpie")'

Change-Id: If3664914cabb092e0c68bd09365690dea2042681
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>