perf, sched migration: Librarize the GUI class

Export the GUI facility in the common library path. It is
going to be useful for other scheduler views.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Nikhil Rao <ncrao@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>