arm64: dts: qcom: sdm660-xiaomi-lavender: Add PWRKEY and RESIN

This enables the volume down key as well as the power button.

Reviewed-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Signed-off-by: Dang Huynh <danct12@riseup.net>
Reviewed-by: Caleb Connolly <caleb@connolly.tech>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211120214227.779742-5-danct12@riseup.net