add daemon mode support to pulseaudio

pulseaudio documentation recommends not using the daemon mode unless you
are on a headless system, but since that is the common case for a
buildroot installation, install the related user and groups

[Peter: fix typos, ifeq check, unconditionally install into target]
Signed-off-by: Jérémy Rosen <jeremy.rosen@openwide.fr>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>