Sound Blaster 16/AWE32 MPU-401 is now always the less-functional variant like it would be on real hardware and its IRQ is always shared with the sound card;
Standalone MPU-401 is now always the fully functional intelligent mode variant;
Standalone MPU-401 is now always available, even when Sound Blaster 16/AWE32 is in use;
Cleaned up sound/midi.c and win/win_midi.c.