BT: Added new file btif_multi_hf.c

The new file contents are copied from Aosp
btif_hf.c file revision 5738f83a. This file
will be used for code modifications for Multi
HF implementation.

Change-Id: I8ba7f343cf85f9d78334a86087bca6942cc735c7
Bluetooth: Changes to implement A2DP Sink Support

 - changes in core stack and adaptation layer
 - awareness of sep type

CRs-Fixed: 580884

Change-Id: I9affefdd2d00597545e49c593ef3bddb110d4c9c
Bluetooth: link audioTrack and sbc decoder

 - load sbc decoder library dynammically
 - interaction with audiotrack module
 - buffering mechanism
 - feturize for OSS builds

CRs-Fixed: 580884

Change-Id: I48373c77a02746f406f4a9c790d36dcd4924558c