perf evsel: Introduce perf_evlist

Killing two more perf wide global variables: nr_counters and evsel_list
as a list_head.

There are more operations that will need more fields in perf_evlist,
like the pollfd for polling all the fds in a list of evsel instances.

Use option->value to pass the evsel_list to parse_{events,filters}.

LKML-Reference: <new-submission>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>