perf tests: Add missing counts.h

Those are getting counts.h via evsel.h, that don't strictly need
counts.h, just forward declarations for some structs, so add it here
before we remove it from there.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-phldqlfxxu563txja7evd4zt@git.kernel.org


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