package/mediastreamer: simplify alsa-lib feature selection

Instead of having the user need to figure out that 2 alsa-lib features
are needed for mediastreamer ALSA support, have the top-level pulseaudio
option select the relevant alsa-lib features, when alsa-lib is enabled
as already done for pulseaudio in commit
97cd3680

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>