backlight: qcom-wled: Add PMI8950 compatible

PMI8950 contains WLED of version 4. Add support for it to the driver.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221226-msm8953-6-2-wled-v1-1-e318d4c71d05@z3ntu.xyz