A2DP: Default to use SBC 48K sampling frequency for TARGET_FLOSS

Currently the default is 44100 and can be changed per user preference.
This makes the default to be 48K if possible to avoid redundant
reconfig.

Bug: 333344362
Bug: 384648601
Test: mmm packages/modules/Bluetooth
Tag: #floss
Flag: EXEMPT, Floss-only change
Change-Id: Ie7597aea3e6a38aaea6d51594bf7785d5607a71a