arm64: dts: qcom: pmi8998: add flash LED controller

Qualcomm PMIC PMI8998 has a 3 channel flash LED driver which is used
by many phones for 1 or 2 flash LEDs. Each LED can be used in flash mode
or torch mode. Add the flash LED controller node to PMI8998 DTS.

Signed-off-by: Dylan Van Assche <me@dylanvanassche.be>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230518133113.273880-3-me@dylanvanassche.be