Make use of the newly added MIDI function in f_midi.c and strip down
the MIDI gadget code radically. Also use the generic framework function
to avoid code duplication and rename some symbols to bring them in sync
with other code in the gadget framework.

[ balbi@ti.com : fix Section mismatch warnings.
	rebased on top of usb_speed_string() patch to
	avoid conflicts. ]
Signed-off-by: NDaniel Mack <zonque@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: NFelipe Balbi <balbi@ti.com>

This patch adds f_midi.c to implement a USB gadget function that works
with the composite framework, so it can be combined with other USB
functions.

The code for the ALSA/MIDI logic was taken from the midi device gadget,
other parts have been rewritten to benefit from the dynamic descriptor
allocation features.

This was successfully tested on an OMAP3 board.
Signed-off-by: NDaniel Mack <zonque@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: NFelipe Balbi <balbi@ti.com>