dt-bindings: backlight: qcom-wled: Add PM6150L compatible

Document the compatible for the wled block found in PM6150L.

Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20211229170358.2457006-2-luca.weiss@fairphone.com