audio policy: introduce audio route concept

As a preambule of introduction of topology concept within
audio policy configuration file, this patch introduces the notion
of audio route, i.e. a link between one sink and one or more sources.
This link may be shareable (mix) or mutual exclusive (mux).

From this route concept, and in order to keep backward compatibility,
the supported device of ioprofile (what will become AudioMixPort) must
be updated.

Change-Id: If078830dbe74b003be4a64c584521df481101294
Signed-off-by: François Gaffie <francois.gaffie@intel.com>