perf tools: Fix parallel build

perf tools: Fix parallel build

Parallel builds of perf were failing for me on a 32p box, with:

    * new build flags or prefix
util/pmu.l:7:23: error: pmu-bison.h: No such file or directory

...

make: *** [util/pmu-flex.o] Error 1
make: *** Waiting for unfinished jobs....

This can pretty quickly be seen by adding a sleep in front of the bison
calls in tools/perf/Makefile and running make -j4 on a smaller box i.e.:

	sleep 10; $(QUIET_BISON)$(BISON) -v util/pmu.y -d -o $(OUTPUT)util/pmu-bison.c

Adding the following dependencies fixes it for me.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/505BD190.40707@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>