Route audio to connected A2DP headset on turn on

If BT is connected after FM app launch and then FM is turned off and then
turned on, audio gets routed to wired headset. Check if A2DP device is
connected every time FM is turned on. Also set the UI icon to correct
image.

CRs-Fixed: 996689
Change-Id: I7314075f1652a1b99b906b674a98dfc12179e9cf