Optionally emit LPCM audio instead of using AAC in wifi display code

related-to-bug: 7248248

May decrease power usage at the cost of significantly increasing audio bitrate.

Use "adb shell setprop media.wfd.use-pcm-audio true"

to turn it on (must be done before connecting).

Change-Id: I7ebeadf3209e01522a2644948287b23d7c383c7e