arm64: dts: qcom: msm8939-longcheer-l9100: Add rear flash

The phone has a Silergy SY7802 flash LED controller.

Signed-off-by: André Apitzsch <git@apitzsch.eu>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Link: https://lore.kernel.org/r/20240624-sy7802-v5-3-7abc9d96bfa6@apitzsch.eu


Signed-off-by: Bjorn Andersson <andersson@kernel.org>