[FM] "Speaker on/headset" should not be available while BT earphone is connected

Launch FM Radio and play -> Turn on BT and connect with
BT earphone -> Enter FM again and check "Speaker on/headset"
, "Speaker on/headset" will be available.

The fix is to also check BT headset is connected or not when
enabling menu item.

Bug 18795153

from: https://partner-android-review.googlesource.com/#/c/192377/2



Change-Id: Ia6d78b85563389f193860820447273a27e76d050
Signed-off-by: Benson Huang <benson.huang@mediatek.com>