perf evsel: Introduce perf_evsel__{in,ex}it

Out of the {con,des}structor, as in interpreted language bindings we will
need to go back from the wrapper object to the real thing. In that case
using container_of will save us to have an extra pointer in the perf_evsel
struct.

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