agl-service-radio: Rework 4A support

Updates for changes to the binding to directly support 4A:
- the over-ride of the output sink is no longer required
- building now always requires gstreamer-1.0
- pulseaudio is now only required when building for non-4A
- set HAVE_4A_FRAMEWORK when building for 4A, as is done for
  the mediaplayer binding

Change-Id: Id0657a5a760a2dff33a84857ba206e92c640b10d
Signed-off-by: Scott Murray <scott.murray@konsulko.com>