perf evlist: Show event attribute details

There was no easy way to see the frequency used, and with the change of
default, we better provide one.

[root@sandy linux]# perf evlist -F
cycles: sample_freq=4000
[root@sandy linux]# perf evlist -v
cycles: sample_freq=4000, size: 80, sample_type: 391, read_format: 7, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, sample_id_all: 1, exclude_guest: 1
[root@sandy linux]#

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-e1p9poez3nwrgycbmwqmhlsu@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>