arm64: dts: qcom: qcs6490-rb3gen2: Enable PWR/VOL keys

arm64: dts: qcom: qcs6490-rb3gen2: Enable PWR/VOL keys

RB3Gen2 has three tiny buttons located under the blue USB-A ports.
They're all connected through the various PMICs and are used for
volume and power.

Describe them.

Signed-off-by: Konrad Dybcio <quic_kdybcio@quicinc.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@oss.qualcomm.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20241004-rb3gen2-pwr-vol-keys-v1-1-4b1859c7cc4f@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>