FM: lower FM volume when AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK received

lower FM Volume in case of AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK and
restore the original volume level when AUDIOFOCUS_GAIN received.

CRs-Fixed: 2469991
Change-Id: Ie5b55999a097f1944552d06009ee012f4e1fb219