perf tools: Convert to GTK2_SUPPORT

For building perf without gtk+2, we can set NO_GTK2=1 as a argument of
make.  It then defines NO_GTK2_SUPPORT macro for C code to do the
proper handling.  However it usually used in a negative semantics -
e.g. #ifndef - so we saw double negations which can be misleading.
Convert it to a positive form to make it more readable.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1348824728-14025-8-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>