omxaudiosink: Implements OpenMAX based audio sinks

omxaudiosink: Implements OpenMAX based audio sinks

Provides omxanalogaudiosink and omxhdmiaudiosink elements on
the Raspberry PI.

- omxanalogaudiosink is capable to render raw mono or stereo audio
through the jack output.
- omxhdmiaudiosink is capable to render raw audio up to 8 channels
and transmit ac3/dts(IEC 61937) through the HDMI output.
- sinks provide a clock derived from rendered samples
- sinks support the GstStreamVolume interface by implementing
the volume and mute properties.

https://bugzilla.gnome.org/show_bug.cgi?id=728962