Use dmix/dsnoop for maestro3 boards

Use dmix/dsnoop for maestro3 boards.  Although maestro3 has multiple
playback capability, it supports only two streams (with the currently
available firmware).

src/conf/cards/Maestro3.conf

@@ -11,3 +11,27 @@ Maestro3.pcm.front.0 {
 	card $CARD
 	device 0
 }	
+
+# default with dmix/dsnoop
+Maestro3.pcm.default {
+	@args [ CARD ]
+	@args.CARD {
+		type string
+	}
+	type asym
+	playback.pcm {
+		type plug
+		slave.pcm {
+			@func concat
+			strings [ "dmix:" $CARD ]
+		}
+	}
+	capture.pcm {
+		type plug
+		slave.pcm {
+			@func concat
+			strings [ "dsnoop:" $CARD ]
+		}
+	}
+}
+