BT-Audio: Keep track of Active TWS+ EB device in BTHelper

Keep track of active TWS+ EB device in MM Audio module
based on device connect/disconnect events as part of
Active device update. This device tracking will help us
to make decision for Audio updates regarding reconfig
should be done OR not based on EBs transition use-case.

CRs-Fixed: 2717923
Change-Id: I2df8447acb1d8e1b843a49906f2f3e3993dee5d6