oxygen: add channel status controls

Add mixer controls to manage the S/PDIF channel status bits.

src/conf/cards/CMI8788.conf

@@ -2,8 +2,6 @@
 # Configuration for the CMI8788 chip
 #
 
-# TODO: add hooks for SPDIF mixer controls
-
 <confdir:pcm/front.conf>
 
 CMI8788.pcm.front.0 {
@@ -126,10 +124,26 @@ CMI8788.pcm.iec958.0 {
 	}
 	type asym
 	playback.pcm {
+		type hooks
+		slave.pcm {
 			type hw
 			card $CARD
 			device 1
 		}
+		hooks.0 {
+			type ctl_elems
+			hook_args [
+				{
+					interface PCM
+					device 1
+					name "IEC958 Playback PCM Stream"
+					lock true
+					preserve true
+					value [ $AES0 $AES1 $AES2 $AES3 ]
+				}
+			]
+		}
+	}
 	capture.pcm {
 		type hw
 		card $CARD