perf mem amd: Fix perf_pmus__num_mem_pmus()

perf mem/c2c on AMD internally uses IBS OP PMU, not the core PMU. Also,
AMD platforms does not have heterogeneous PMUs.

Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ali Saidi <alisaidi@amazon.com>
Cc: Ananth Narayan <ananth.narayan@amd.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Santosh Shukla <santosh.shukla@amd.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Link: https://lore.kernel.org/r/20230615051700.1833-3-ravi.bangoria@amd.com


[ Added the improved comment for perf_pmus__num_mem_pmus() as b4 didn't from the per-patch (not series) newer version ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>