hal: fix no audio in fm playback usecase

- FM playback is broken since incorrect pcm id is used. Fix
by adding the missing usecase to the usecase index table.

- Remove headphones from backend default table as it incorrectly
appends headphones to the usecase name even when independent backend
for headphones is not enabled.

Change-Id: I7bfa3cd3516c37404570a61586eff0a4e419fb25