[ALSA] Add description of imac-intel model

Added the description of missing imac-intel model for hda-intel driver.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NJaroslav Kysela <perex@suse.cz>

Documentation/sound/alsa/ALSA-Configuration.txt

@@ -909,6 +909,7 @@ Prior to version 0.9.0rc4 options had a 'snd_' prefix. This was removed.
 	  macbook	Intel Mac Book
 	  macbook-pro-v1 Intel Mac Book Pro 1st generation
 	  macbook-pro	Intel Mac Book Pro 2nd generation
+	  imac-intel	Intel iMac
 
 	STAC9202/9250/9251
 	  ref		Reference board, base config