dt-bindings: leds-qcom-lpg: Add qcom,pmk8550-pwm compatible string

Add qcom,pmk8550-pwm compatible string for the Qualcomm Technologies, Inc.
PMK8550 PMIC which has two high resolution PWM channels.

Signed-off-by: Anjelique Melendez <quic_amelende@quicinc.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230407223849.17623-2-quic_amelende@quicinc.com