Add a new field "direction" to snd_seq_port_info for allowing a client
to tell the expected direction of the port access.  A port might still
allow subscriptions for read/write (e.g. for MIDI-CI) even if the
primary usage of the port is a single direction (either input or
output only).  This new "direction" field can help to indicate such
cases.

When the direction is unspecified at creating a port and the port has
either read or write capability, the corresponding direction bits are
set automatically as default.
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230523075358.9672-29-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>