seq: Add API helper functions for creating UMP Endpoint and Blocks

seq: Add API helper functions for creating UMP Endpoint and Blocks

For making it easer for applications to create a virtual UMP Endpoint
and UMP blocks, add two API helper functions.

snd_seq_create_ump_endpoint() creates (unsurprisingly) a UMP Endpoint,
based on the given snd_ump_endpoint_info_t information.  The number of
(max) UMP groups belonging to this Endpoint has to be specified.
This function sets up the Endpoint info on the sequencer client, and
creates a MIDI 2.0 UMP port as well as UMP Group ports automatically.
The name of the sequencer client is updated from the Endpoint name,
too.

After creating a UMP Endpoint, create each UMP Block via
snd_seq_create_ump_block() function with a snd_ump_block_info_t info.
The associated groups for each block have to be specified there.
The port names and capability bits are updated accordingly after
setting each block information.

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