On the Intel Sapphire Rapids server, an auxiliary event has to be
enabled simultaneously with the load latency event to retrieve complete
Memory Info.

Add X86 specific perf_mem_events__name() to handle the auxiliary event.

- Users are only interested in the samples of the mem-loads event.
  Sample read the auxiliary event.

- The auxiliary event must be in front of the load latency event in a
  group. Assume the second event to sample if the auxiliary event is the
  leader.

- Add a weak is_mem_loads_aux_event() to check the auxiliary event for
  X86. For other ARCHs, it always return false.

Parse the unique event name, mem-loads-aux, for the auxiliary event.

Committer notes:

According to 61b985e3 ("perf/x86/intel: Add perf core PMU
support for Sapphire Rapids"), ENODATA is only returned by
sys_perf_event_open() when used with these auxiliary events, with this
in evsel__open_strerror():

       case ENODATA:
               return scnprintf(msg, size, "Cannot collect data source with the load latency event alone. "
                                "Please add an auxiliary event in front of the load latency event.");

This is Ok at this point in time, but fragile long term, I pointed this
out in the e-mail thread, requesting a follow up patch to check if
ENODATA is really for this specific case.

Fixed up sizeof(MEM_LOADS_AUX_NAME) bug pointed out by Namhyung.
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20210205152648.GC920417@kernel.org
Link: http://lore.kernel.org/lkml/1612296553-21962-3-git-send-email-kan.liang@linux.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>