perf tools: Move GTK+ bits to tools/perf/ui/gtk directory

perf tools: Move GTK+ bits to tools/perf/ui/gtk directory

Move those files to new directory in order to be prepared to
further UI work. Makefile and header file pathes are adjusted
accordingly. Also fix a build breakage if NO_GTK2=1 is given.

Signed-off-by: Namhyung Kim <namhyung.kim@lge.com>
Suggested-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl
Link: http://lkml.kernel.org/r/1333523765-12092-1-git-send-email-namhyung.kim@lge.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>