alsactl: Add path condition to alsa-store and alsa-restore services

alsactl: Add path condition to alsa-store and alsa-restore services

With alsa-restore.service and alsa-store.service, systemd invokes
alsactl at boot and shutdown times.  When this is invoked on a system
without sound cards, it results in an ugly error message from alsact

  /usr/sbin/alsactl: save_state:1590: No soundcards found...
  return code is "19"

Add ConditionPathExistsGlob checks of /dev/snd/control* devices for
avoiding unnecessary invocations of alsactl on such a system.

Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=940950
Signed-off-by: Takashi Iwai <tiwai@suse.de>