Pulseaudio configuration fixes

Some fixes to work when 4A is enabled:
- Simplified the echo that adds /etc/pulse/default.d to
  /etc/pulse/default.pa, as it was resulting in "-e -n" in the file
  sometimes for reasons unknown.
- PulseAudio does not like the /etc/pulse/default.d directory being
  empty, and additionally it was realized that the module unloads that
  are in module-router.pa are useful in all our usecases and should
  likely always be present.  To kill two birds with one stone, the
  unload lines have been moved to a 10-unload-modules.pa file that
  is installed by the pulseaudio bbappend, and those lines have been
  removed from the module-router.pa files, which has been renamed to
  20-module-router.pa so that ordering will be maintained if someone
  needs to reenable it.

Change-Id: I70cd1d0dfc596b894009c1bdd7520ffe6394e60e
Signed-off-by: Scott Murray <scott.murray@konsulko.com>