backlight: qcom-wled: Add callback functions

Add wled_cabc_config, wled_sync_toggle, wled_ovp_fault_status
and wled_ovp_delay and wled_auto_detection_required callback
functions to prepare the driver for adding WLED5 support.

Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>