Change sendVolumeKeyEvent condition

[Description]
In 5c03084e
CEC volume control is changed to use full volume control

However, if ARC is not connected due to :
 - AVR connecting to non-ARC port of TV
 - Specific AVR configuration

System audio mode is on, but volume control feature doesn't work

We should check system audio and volume control status instead of check
whether current device is a full volume device when trying to notify CEC
framework about the volume change event

[Test Report]
Test with TV connecting AVR : Denon 2400/ SR6013
- connected to non ARC port, volume control PASS
- connected to ARC port, volume control PASS

Run CTS PASS
- android.hdmicec.cts.common.HdmiCecSystemAudioControlTest
- android.hdmicec.cts.tv.HdmiCecRemoteControlPassThroughTest
(#cect_11_1_13_4_RemoteControlMessagesToAudioSystem)

Bug: 253189182
Change-Id: If4b3ad7b1af6246e0ff935e1eb1401f1736e5ff2