ALSA: seq: Allow system notification in atomic

Currently the system notification helper assumes only the non-atomic
delivery.  For allowing an event delivery in non-atomic context, add
the atomic flag to the helper function.

This is a preliminary change for the support of UMP EP/FB
notification.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20250110155943.31578-8-tiwai@suse.de