libhardware: Add keys to support FM

Add keys for FM device and FM volume

Change-Id: Ib26df18a72f96bf19d577d99e93296a37f04ed7b
(cherry picked from commit 1dd30a530cf3b595d9877d0d15739b2b1b76889a)
(cherry picked from commit 2599b75a58206332ea00206171dfff078bda20ff)
(cherry picked from commit 0a3f3c974406228d6541a2df6d38b42fdbfd790b)

Conflicts:
	include/hardware/audio.h