backlight: qcom-wled: Restructure the driver for WLED3

Restructure the driver to add the support for new WLED
peripherals.

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