package/pulseaudio: simplify alsa-lib feature selection

Instead of having the user need to figure out that 3 alsa-lib features
are needed for pulseaudio ALSA support, have the top-level pulseaudio
option select the relevant alsa-lib features, when alsa-lib is
enabled.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>