perf bpf: Rename 'cpu' to 'cpu_map_idx'

perf bpf: Rename 'cpu' to 'cpu_map_idx'

Synchronize the caller in evsel with the called function.

Shorten 3 lines of code in bperf_read by using
perf_cpu_map__for_each_cpu().

This code is frequently using variables named cpu as cpu map indices,
which doesn't matter as all CPUs are in the CPU map. It is strange in
some cases the cpumap is used at all.

Committer notes:

Found when building with BUILD_BPF_SKEL=1:

Remove unused 'num_cpu' variable in bperf__read().

Make 'j' an 'int' as it is used in perf_cpu_map__for_each_cpu() to compare against an 'int'

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Riccardo Mancini <rickyman7@gmail.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Vineet Singh <vineet.singh@intel.com>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: zhengjun.xing@intel.com
Link: https://lore.kernel.org/r/20220105061351.120843-45-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>