Major sound system update

[Francois Tigeot]

Hi,

The sound system has been completely upgraded from FreeBSD 11-CURRENT.

A complete world + kernel rebuild sequence is required on -master.


The previous version was based on the FreeBSD 6.x branch, circa 2007
and was starting to show its age.


Among many improvements, we get:

* Much smarter volume controls

* Improved HDMI/DisplayPort audio support

* An easy way to switch the default sound device with the
  hw.snd.default_unit sysctl

* HTML5/Youtube videos should play with sound out of the box


On top of the FreeBSD code, we also have additional support for the
Acer C720 Chromebook family of laptops.

-- 
Francois Tigeot