USB-Audio: Do not use 4ch playback stream for stereo Focusrite Scarlet devices

Link: alsa-project#309
Link: alsa-project#329
Link: alsa-project#314
Signed-off-by: Jaroslav Kysela <[email protected]>

Author: perexg

ucm2/USB-Audio/Focusrite/Scarlett-2i-HiFi.conf

@@ -1,19 +1,6 @@
 Include.pcm_split.File "/common/pcm/split.conf"
 
 Macro [
-	{
-		SplitPCM {
-			Name "scarlett2i_stereo_out"
-			Direction Playback
-			Format S32_LE
-			Channels 2
-			HWChannels 4
-			HWChannelPos0 FL
-			HWChannelPos1 FR
-			HWChannelPos2 FL
-			HWChannelPos3 FR
-		}
-	}
 	{
 		SplitPCM {
 			Name "scarlett2i_mono_in"
@@ -27,21 +14,54 @@ Macro [
 	}
 ]
 
+If.2i4 {
+	Condition {
+		Type String
+		String1 "${var:PlaybackChannels}"
+		String2 "4"
+	}
+	True.Macro [
+		{
+			SplitPCM {
+				Name "scarlett2i_stereo_out"
+				Direction Playback
+				Format S32_LE
+				Channels 2
+				HWChannels 4
+				HWChannelPos0 FL
+				HWChannelPos1 FR
+				HWChannelPos2 FL
+				HWChannelPos3 FR
+			}
+		}
+	]
+}
+
 SectionDevice."Line1" {
 	Comment "${var:Playback1Name}"
 
 	Value {
 		PlaybackPriority 200
 	}
-	Macro.pcm_split.SplitPCMDevice {
-		Name "scarlett2i_stereo_out"
-		Direction Playback
-		HWChannels 4
-		Channels 2
-		Channel0 0
-		Channel1 1
-		ChannelPos0 FL
-		ChannelPos1 FR
+	If.2i4 {
+		Condition {
+			Type String
+			String1 "${var:PlaybackChannels}"
+			String2 "4"
+		}
+		True.Macro.pcm_split.SplitPCMDevice {
+			Name "scarlett2i_stereo_out"
+			Direction Playback
+			HWChannels 4
+			Channels 2
+			Channel0 0
+			Channel1 1
+			ChannelPos0 FL
+			ChannelPos1 FR
+		}
+		False.Value {
+			PlaybackPCM "hw:${CardId}"
+		}
 	}
 }