sound feature refactoring

Split package lists:

- base alsa packages (also needed in pulseaudio-based installations)
- additional alsa packages (needed only if not using pulseaudio)
- pulseaudio packages

features.in/sound/config.mk

@@ -1,11 +1,16 @@
 +pulse: use/sound/pulse; @:
++alsa:  use/sound/alsa; @:
 
 # "bare" ALSA (which is good enough for many of us) with persistent levels
 use/sound:
 	@$(call add_feature)
 	@$(call add,THE_KMODULES,alsa sound)
-	@$(call add,THE_PACKAGES,amixer alsa-utils aplay udev-alsa)
+	@$(call add,THE_LISTS,sound/base)
+
+# ALSA only sound (additional utils needed if using pulseaudio)
+use/sound/alsa: use/sound
+	@$(call add,THE_PACKAGES,apulse)
 
 # PulseAudio (useful for per-app levels, dynamic devices and networked sound)
 use/sound/pulse: use/sound
-	@$(call add,THE_LISTS,pulseaudio)
+	@$(call add,THE_LISTS,sound/pulseaudio)

pkg.in/lists/sound/base

@@ -0,0 +1,4 @@
+amixer
+alsa-utils
+aplay
+udev-alsa