Looks like util/debug.h was indirectly included before and is no longer
included now. pr_debug is left undefined and the build of perf tool
fails on Powerpc.

Explicitly include util/debug.h.
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Michael Ellerman <michaele@au1.ibm.com>
Link: http://lkml.kernel.org/r/20140807072700.GA17623@us.ibm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>