arm64: dts: qcom: msm8916-longcheer-l8910: Add rear flash

The phone has a Silergy SY7802 flash LED controller.

Tested-by: Stéphane Martins <stemartins@proton.me>
Signed-off-by: André Apitzsch <git@apitzsch.eu>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Link: https://lore.kernel.org/r/20240722-x5_sy7802-v1-1-b2ffeeaf8d2d@apitzsch.eu


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