This is a code refactoring for abstracting the rawmidi access to the
UMP's own helpers.  It's a preliminary work for the later code
refactoring of the UMP layer.

Until now, we access to the rawmidi substream directly from the
driver via rawmidi access helpers, but after this change, the driver
is supposed to access via the newly introduced snd_ump_ops and
receive/transmit via snd_ump_receive() and snd_ump_transmit() helpers.
As of this commit, those are merely wrappers for the rawmidi
substream, and no much function change is seen here.
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230523075358.9672-14-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>