Renamed "upstart" dir to "init". Pulled the main script to a separate
file which is shared between systemd and Upstart.

BUG=chromium:583671
CQ-DEPEND=CL:373478
TEST=Checked that the sound works.

Change-Id: I643b1fd151f22e9c6a56cfb96eea6fa9d6556eb7
Reviewed-on: https://chromium-review.googlesource.com/373379


Commit-Ready: Sabin Floares <sabin.floares@intel.com>
Tested-by: Sabin Floares <sabin.floares@intel.com>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>