perf python: Add basic PMU abstraction and pmus sequence

perf python: Add basic PMU abstraction and pmus sequence

Add an ability to iterate over PMUs and a basic PMU type then can just
show the PMU's name.

An example usage:
```
$ python
Python 3.12.9 (main, Feb  5 2025, 01:31:18) [GCC 14.2.0] on linux
>>> import perf
>>> list(perf.pmus())
[pmu(cpu), pmu(breakpoint), pmu(cstate_core), pmu(cstate_pkg),
pmu(hwmon_acpitz), pmu(hwmon_ac), pmu(hwmon_bat0),
pmu(hwmon_coretemp), pmu(hwmon_iwlwifi_1), pmu(hwmon_nvme),
pmu(hwmon_thinkpad), pmu(hwmon_ucsi_source_psy_usbc000_0),
pmu(hwmon_ucsi_source_psy_usbc000_0), pmu(i915), pmu(intel_bts),
pmu(intel_pt), pmu(kprobe), pmu(msr), pmu(power), pmu(software),
pmu(tool), pmu(tracepoint), pmu(uncore_arb), pmu(uncore_cbox_0),
pmu(uncore_cbox_1), pmu(uncore_cbox_2), pmu(uncore_cbox_3),
pmu(uncore_cbox_4), pmu(uncore_cbox_5), pmu(uncore_cbox_6),
pmu(uncore_cbox_7), pmu(uncore_clock), pmu(uncore_imc_free_running_0),
pmu(uncore_imc_free_running_1), pmu(uprobe)]
```

Committer testing:

One has to set PYTHONPATH to the build directory beforehand:

  $ export PYTHONPATH=/tmp/build/perf-tools-next/python/
  $ python
  Python 3.13.7 (main, Aug 14 2025, 00:00:00)
                 [GCC 15.2.1 20250808 (Red Hat 15.2.1-1)] on linux
  >>> import perf
  >>> list(perf.pmus())
  [pmu(cpu), pmu(amd_df), pmu(amd_iommu_0), pmu(amd_l3), pmu(amd_umc_0),
   pmu(breakpoint), pmu(hwmon_amdgpu), pmu(hwmon_amdgpu), pmu(hwmon_k10temp),
   pmu(hwmon_nvme), pmu(hwmon_r8169_0_e00_00), pmu(ibs_fetch), pmu(ibs_op),
   pmu(kprobe), pmu(msr), pmu(power), pmu(power_core), pmu(software),
   pmu(tool), pmu(tracepoint), pmu(uprobe)]
  >>>

Reviewed-by: Howard Chu <howardchu95@gmail.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Chun-Tse Shao <ctshao@google.com>
Cc: Collin Funk <collin.funk1@gmail.com>
Cc: Dr. David Alan Gilbert <linux@treblig.org>
Cc: Gautam Menghani <gautam@linux.ibm.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: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Falcon <thomas.falcon@intel.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Weilin Wang <weilin.wang@intel.com>
Cc: Xu Yang <xu.yang_2@nxp.com>
Link: https://lore.kernel.org/r/20250819013941.209033-4-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>