The AUDIO_SUPPORT target feature is replaced in openwrt.git by an
audio-support package, which allocates the audio, audio-capture and midi
groups and installs the hotplug rules that put the ALSA nodes into them.
A target feature said only that the SoC family might have a sound card;
the package says that this image has one.
Depend on the package where the feature was tested, and read
CONFIG_PACKAGE_audio-support where mpd tested the feature at build time.
Signed-off-by: Daniel Golle <daniel@makrotopia.org>