Integration of the LDAC codec for A2DP source

The codec can be used if the encoding shared library is installed
on the device:
 libldacBT_enc.so

Also, increased the maximum number of SEPs AVDT_NUM_SEPS from 3
to 6 to accomodate Sink devices that support more than 3 codecs.

Test: A2DP streaming to LDAC headsets
Bug: 30958229
Change-Id: I114c3e6be2ebe1ac8aece62a3146637d37cd938e