perf evlist: Introduce 'disable' method

To remove the last case of access to the FD() macro outside the library.

Inspired by a patch by Borislav that moved the FD() macro to util.h, for
namespace concerns I rather preferred to constrain it to ev{sel,list}.c.

Cc: Borislav Petkov <bp@amd64.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
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-qn893qsstcg366tkucu649qj@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>