perf evsel: Move config terms to a separate header

Further reducing the size of util/evsel.h.

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-20zr7di9eynm0272mtjfdhfc@git.kernel.org


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