backlight: qcom-spmi-wled: Add torch and flash support for WLED5

WLED5 peripherals in PM8150L supports preflash(torch) and flash
functionality. Add support for brightness control of flash/torch
devices in them dynamically.

To turn on torch,
echo 60 > /sys/class/wled_torch/brightness
echo 1 > /sys/class/wled_switch/brightness

To turn off torch,
echo 0 > /sys/class/wled_switch/brightness
echo 0 > /sys/class/wled_torch/brightness

Change-Id: Ibb6f2f9a97ffe5d17ebbb26ae4103c4afb37c9a8
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>