Support multi-card/device for direct plugins

- Support multi-card/device for dmix/dsnoop/dshare plugins
  The unique ipc key is calculated based on card/device/sub index

- Clean up and share the code among all d* plugins

- Refer the defaults.pcm.* configuration
  The base ipc_key number, ipc_gid and ipc_perm are referred.

src/conf/alsa.conf

@@ -54,6 +54,9 @@ defaults.pcm.card 0
 defaults.pcm.device 0
 defaults.pcm.subdevice -1
 defaults.pcm.nonblock 1
+defaults.pcm.ipc_key 5678293
+defaults.pcm.ipc_gid audio
+defaults.pcm.ipc_perm 0660
 defaults.pcm.front.card defaults.pcm.card
 defaults.pcm.front.device defaults.pcm.device
 defaults.pcm.rear.card defaults.pcm.card

src/conf/pcm/dmix.conf

@@ -25,9 +25,18 @@ pcm.!dmix {
 		default 48000
 	}
 	type dmix
-	ipc_key 5678293
-	ipc_gid audio
-	ipc_perm 0660
+	ipc_key {
+		@func refer
+		name defaults.pcm.ipc_key
+	}
+	ipc_gid {
+		@func refer
+		name defaults.pcm.ipc_gid
+	}
+	ipc_perm {
+		@func refer
+		name defaults.pcm.ipc_perm
+	}
 	slave {
 		pcm {
 			type hw

src/conf/pcm/dsnoop.conf

@@ -25,9 +25,18 @@ pcm.!dsnoop {
 		default 48000
 	}
 	type dsnoop
-	ipc_key 5778293
-	ipc_gid audio
-	ipc_perm 0660
+	ipc_key {
+		@func refer
+		name defaults.pcm.ipc_key
+	}
+	ipc_gid {
+		@func refer
+		name defaults.pcm.ipc_gid
+	}
+	ipc_perm {
+		@func refer
+		name defaults.pcm.ipc_perm
+	}
 	slave {
 		pcm {
 			type hw