perf pmu: Remove use of perf_cpu_map__read()

perf pmu: Remove use of perf_cpu_map__read()

Remove use of a FILE and switch to reading a string that is then
passed to perf_cpu_map__new().

Being able to remove perf_cpu_map__read() avoids duplicated parsing logic.

Reviewed-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ben Gainey <ben.gainey@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Kyle Meyer <kyle.meyer@hpe.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241206044035.1062032-6-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>