dt-bindings: leds: qcom-lpg: Add compatible for PM660L LPG block

Document the availability of an LPG configuration for the PM660L PMIC in
the Qualcomm Light Pulse Generator driver.

Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220719211848.1653920-1-marijn.suijten@somainline.org