pulseaudio: configure it to be compatible with the android-audiosystem

* Pulseaudio needs to be start only when the android mediaserver is running as otherwise
  it will hang while accessing the audioflinger service through android-audiosystem
* We're overriding the default configuration with our own variant which will be extended
  soon to support the webOS audio system.
* We can't use udev based module autodetection while configuring manual alsa sink/source
  as this leads to access pulseaudio the alsa card provided by the device twice and having
  our kernel oopsing.
* always start in system mode

Signed-off-by: Simon Busch <morphis@gravedo.de>
android-audiosystem: install needed alsa configuration file

Signed-off-by: Simon Busch <morphis@gravedo.de>