perf test: Use shelldir to refer perf source location

perf test: Use shelldir to refer perf source location

It uses tools/perf/include which assumes it's running from the root of
the linux kernel source tree.  But you can run perf from other places
like tools/perf, then the include path won't match.  We can use the
shelldir variable to locate the test script in the tree.

  $ cd tools/perf

  $ ./perf test dlfilter
   63: dlfilter C API                                                  : Ok
  101: perf script --dlfilter tests                                    : Ok

Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>