alsactl: Manage both save and restore in a single unit

alsactl: Manage both save and restore in a single unit

With RemainAfterExit=true, we can manage both save and restore of the
card state in a single unit file.  This will fix also the case where
systemd reloads the service; with two individual units, it will
restore the previous state before saving, and may lead to inconsistent
state suddenly.

Also fix alsa-state.service as well to make both start and stop
working in a simpler way.

Bugzilla: https://bugzilla.novell.com/show_bug.cgi?id=929619
Signed-off-by: Takashi Iwai <tiwai@suse.de>