perf version: Add a feature for libpfm4

If perf is built with libpfm4 (LIBPFM4=1) then advertise it in perf -vv.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20201019232545.4047264-1-irogers@google.com


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