AVRCP(T): Add support for AVRCP 1.6

AVRCP(T): Add support for AVRCP 1.6

This patch adds supports for following AVRCP 1.6 target features:
    - Get Total Number of Items
    - Cover Art Feature

CRs-Fixed: 715683

AVRCP1.6: Reset Cover Art supported feature bit

Reset Cover Art supported feature bit in SDP record if
fallback to lower version.
Change-Id: I47bdc5dcbc777ba3afb90be1d52b0f6a152dde7b
CRs-Fixed: 956637

Update conf file only if Avrcp 1.5 or 1.6 is enabled

Update conf file only if Avrcp 1.5 or 1.6 is enabled.
CRs-Fixed: 963208

Change-Id: Ib8e81cc57a8060202dbfb2b90b5009f8d504529e

BT-AVRCP: Queue txn labels for same PDU.

If AVRCP CT sends same PDU request multiple times in
quick succession, TG ovewrites the txn label against
that PDU. This causes TG to respond with incorrect
txn labels

Change-Id: I0c9b10f0eb0e7cb695c224d8fe26f5c447ba7d93
CRs-Fixed: 995483

Change-Id: I58ec30ae039f78c59422b5612ebb9ef65a03e2dd