linux-firmware: mediatek: add firmware for mt7668u Bluetooth

Add binary firmware for mt7668u based Bluetooth devices.
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>

WHENCE

@@ -3932,6 +3932,8 @@ Driver: btmtk - MediaTek Bluetooth Driver
 
 File: mediatek/mt7622pr2h.bin
 Version: 20180621204904
+File: mediatek/mt7668pr2h.bin
+Version: 20180517181834
 
 Licence: Redistributable. See LICENCE.mediatek for details.