Bluetooth: Change Sampling Frequency to 48 kHz

Change Default Sampling Frequency to 48 kHz by default to
match Audio Source.
CRs-fixed: 436686
Change-Id: I0a4aa9ca61964e76220c77fa60c281f7a5df58b4
a2dp: Set the default A2DP bitrate to high quality

Allows bluedroid to calculate the proper A2DP bitpool size.
This resolves the main A2DP audio quality issues with Android 4.2,
but does not address the difference in audio output gain/volume as
compared with Android 4.1.

Setting the output volume level to approximately 80% in conjunction
with this change seems to result in comparable audio quality

Change-Id: Ic05c3278ebe9288d00926fab8b7c1a646fd861cd