perf: Update .gitignore file

After a "make tools/perf", git reports the following untracked files:

  tools/perf/feature/
  tools/perf/fixdep
  tools/perf/libtraceevent-dynamic-list

Add these generated files to perf's .gitignore file.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: x86@kernel.org
Link: http://lore.kernel.org/lkml/03acbc6c2fbc72054861f6c301875db75db33030.1567118001.git.jpoimboe@redhat.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>