leds: flash: Add driver to support flash LED module in QCOM PMICs

Add initial driver to support flash LED module found in Qualcomm
Technologies, Inc. PMICs. The flash module can have 3 or 4 channels
and each channel can be controlled indepedently and support full scale
current up to 1.5 A. It also supports connecting two channels together
to supply one LED component with full scale current up to 2 A. In that
case, the current will be split on each channel symmetrically and the
channels will be enabled and disabled at the same time.

Signed-off-by: Fenglin Wu <quic_fenglinw@quicinc.com>
Tested-by: Luca Weiss <luca.weiss@fairphone.com> # sm7225-fairphone-fp4 + pm6150l
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230303095023.538917-2-quic_fenglinw@quicinc.com