ALSA: hda - Add model string for Intel reference board quirk

For allowing user to apply the existing quirk on a machine with a
different SSID, add a new model string entry, alc700-ref.
The quirk itself was introduced in the commit b84e8436: "ALSA:
hda/realtek - Enable jack detection function for Intel ALC700")

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