audio policy: fix regression in incall notification management

Commit 2110e04c introduced a regression preventing ongoing alarms to
be restored when exiting a call and leaving the replacement tone
playing for ever.

Also add missing management of accessibility prompts when entering a
call.

Bug: 21857005.
Change-Id: I4295c791c003db42c0fba9f618e51f60438158d1
1 file changed