HFP: Add support for Multi-HFP (2/2)

* Allocate at most 6 control blocks for btif_hf and bta_ag,
  this limit is defined by BTA_AG_MAX_NUM_CLIENTS
* Allow at most 6 RFCOMM connections to be managed by bta_ag
* Allow at most 6 SDP callbacks for each bta_ag
* Reject incoming SCO connection and do not start outgoing SCO
  connection if not coming from the current active device
* Reject incoming AT+BCC request if the remote device is not an active
  device
* Support only one device by default
* Fixed a bug in BTM_CreateSco where power mode was checked for old
  device and new power mode is set for new device and caused BTM SCO
  state machine to stuck in SCO_ST_PEND_UNPARK mode
* Added logs at failure conditions to be more verbose about connection
  errors and removed logs from non-error conditions to reduce verbosity
  in normal conditions

Bug: 68952570
Test: runtest -j40 bluetooth, native unit tests, HFP regression for 1
      device, simple tests for multiple devices
Change-Id: I97d20f6a126d77a4ef3a0cd1706b48130b4a6aae