perf/x86: Update SNB PEBS constraints

Afaict there's no need to (incompletely) iterate the
MEM_UOPS_RETIRED.* umask state.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1338884803.28282.153.camel@twins


Signed-off-by: Ingo Molnar <mingo@kernel.org>