Handle messages in standby for DeviceDiscoveryAction

The modification of HdmiCecStandbyModeHandler is for processing
DeviceDiscoveryAction on quiescent boot, where the power status
is POWER_STATUS_STANDBY.

Without the modification,<Device vendor ID> and <Report power status>
are not passed to DeviceDiscoveryAction, and CEC framework cannot
establish device information correctly.

Bug: 174982925

Change-Id: Ie0a7ec3892d5f0a97d192b184454c9bde9f92a09