ALSA: ump: Add helper to change MIDI protocol

This is a preliminary patch for MIDI 2.0 USB gadget driver.
Export a new helper to allow changing the current MIDI protocol from
the outside.

Link: https://lore.kernel.org/r/20230621110241.4751-2-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>