perf tools: Add the empty-pmu-events build to .gitignore

The commit 0fe881f1 ("perf jevents: Autogenerate empty-pmu-events.c")
build will generate two files, add them to .gitignore:

	tools/perf/pmu-events/empty-pmu-events.log
	tools/perf/pmu-events/test-empty-pmu-events.c

Signed-off-by: Haiyue Wang <haiyuewa@163.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20241106121254.2869-1-haiyuewa@163.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>