dt-bindings: leds: Add QCOM flash LED controller

Add binding document for flash LED module inside Qualcomm Technologies,
Inc. PMICs.

Signed-off-by: Fenglin Wu <quic_fenglinw@quicinc.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230303095023.538917-3-quic_fenglinw@quicinc.com