arm64: dts: qcom: sdm660-xiaomi-lavender: Add volume up button

This enables the volume up key.

Signed-off-by: Dang Huynh <danct12@riseup.net>
Tested-by: Alexey Minnekhanov <alexeymin@postmarketos.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211121170449.1124048-1-danct12@riseup.net