Make "default" PCM card-specific

"default" PCM can be card-specific.
The definition is moved to pcm/default.conf, and read on-demmand via
aliases.conf.  The card config can override the default config.

src/conf/alsa.conf

@@ -284,38 +284,6 @@ pcm.null {
 	type null
 }
 
-pcm.default {
-	type plug
-	slave.pcm {
-		type hw
-		card {
-			@func getenv
-			vars [
-				ALSA_PCM_CARD
-				ALSA_CARD
-			]
-			default {
-				@func refer
-				name defaults.pcm.card
-			}
-		}
-		device {
-			@func igetenv
-			vars [
-				ALSA_PCM_DEVICE
-			]
-			default {
-				@func refer
-				name defaults.pcm.device
-			}
-		}
-		subdevice {
-			@func refer
-			name defaults.pcm.subdevice
-		}
-	}
-}
-
 # redirect to load-on-demand extended pcm definitions
 pcm.cards cards.pcm
 # some links for easy use
@@ -331,6 +299,7 @@ pcm.surround71 cards.pcm.surround71
 pcm.iec958 cards.pcm.iec958
 pcm.spdif cards.pcm.iec958
 pcm.modem cards.pcm.modem
+pcm.default cards.pcm.default
 
 #
 #  Control interface