backlight: Add support Skyworks SKY81452 backlight driver

Signed-off-by: Gyungoh Yoo <jack.yoo@skyworksinc.com>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Bryan Wu <cooloney@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>