hal: Reset slimbus backend config on A2DP disconnect

This change resets slimbus backend config when A2DP is
disconnected. Existing code relies on stop stream from
framework to reset A2DP backend. Disconnect event coming
before stop stream resets active sessions and hence on
subsequent stop stream, backend config is not reset to
8KHZ. This leads to problems with non-wideband SCO sinks.

Bug: 112342177
Test: Manual MO call test with BMW car kit

Change-Id: I47005be97cb1d6eed1682993532dcc80017066ab
(cherry picked from commit 91c09872640f867da8b0527eaed581557ba9935d)