[ALSA] hda-codec - Add AD1882 codec support

Added AD1882 codec support.  It has currently two models, 3stack and
6stack.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

Documentation/sound/alsa/ALSA-Configuration.txt

@@ -874,6 +874,10 @@ Prior to version 0.9.0rc4 options had a 'snd_' prefix. This was removed.
 	  allout	5-jack in back, 2-jack in front, SPDIF out
 	  auto		auto-config reading BIOS (default)
 
+	AD1882
+	  3stack	3-stack mode (default)
+	  6stack	6-stack mode
+
 	AD1884
 	  N/A