dt-bindings: backlight: qcom-wled: Add WLED5 bindings

Add WLED5 specific bindings.

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