dt-bindings: input: qpnp-power-on: Add qcom,log-kpd-event description

Add support 'qcom,log-kpd-event' property which when enabled causes
KPDPWR status to be logged during driver INIT and runtime when key is
pressed.

Change-Id: Ie8a8068cc8faefdbe678b4e7d11cac179faf01dd