According Realteks own BT drivers firmware RTL8761B is for UART
and RTL8761BU is for USB.

Change existing 8761B to UART and add an 8761BU entry for USB

Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@infinera.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>