ALSA: hda/realtek: Fix add a "ultra_low_power" function for intel reference board (alc256)

Intel requires to enable power saving mode for intel reference board (alc256)

Signed-off-by: PeiSen Hou <pshou@realtek.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200727115647.10967-1-tiwai@suse.de


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