frameworks/base: Add wifi display to fixed volume devices

Wifi display should be treated as device with fixed volume like HDMI.
User should not be able to change the volume on device. Volume
change should be supported only on the end device
CRs-Fixed: 480334

Change-Id: I2e41e9aef01167d1bdca3bca09ed863834dae1d8

Conflicts:
	media/java/android/media/AudioService.java