ARM: dts: msm: Add flash/torch devices for WLED on PM6150L

Add flash and torch device for PM6150L WLED to support front
camera flash on SM6150 platforms. Also specify the number of
LEDs per string to calculate the WLED flash current.

Change-Id: I9d6b8ac1de33af7be7cb3ea4715e982bcf63ec1b
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>