perf pmu: Split perf_pmu__new_alias()

perf pmu: Split perf_pmu__new_alias()

Separate the event parsing code in perf_pmu__new_alias() out into a
separate function __perf_pmu__new_alias() so that code can be called
indepdently.

This is based on an earlier patch from Andi Kleen.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1433921123-25327-5-git-send-email-sukadev@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>