ALSA: seq: Support MIDI 2.0 UMP Endpoint port

This is an extension to ALSA sequencer infrastructure to support the
MIDI 2.0 UMP Endpoint port.  It's a "catch-all" port that is supposed
to be present for each UMP Endpoint.  When this port is read via
subscription, it sends any events from all ports (UMP Groups) found in
the same client.

A UMP Endpoint port can be created with the new capability bit
SNDRV_SEQ_PORT_CAP_UMP_ENDPOINT.  Although the port assignment isn't
strictly defined, it should be the port number 0.

Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230523075358.9672-28-tiwai@suse.de


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