perf parse-events: Prefer sysfs/JSON hardware events over legacy

perf parse-events: Prefer sysfs/JSON hardware events over legacy

It was requested that RISC-V be able to add events to the perf tool so
the PMU driver didn't need to map legacy events to config encodings:
https://lore.kernel.org/lkml/20240217005738.3744121-1-atishp@rivosinc.com/

This change makes the priority of events specified without a PMU the
same as those specified with a PMU, namely sysfs and JSON events are
checked first before using the legacy encoding.

The hw_term is made more generic as a hardware_event that encodes a
pair of string and int value, allowing parse_events_multi_pmu_add to
fall back on a known encoding when the sysfs/JSON adding fails for
core events. As this covers PE_VALUE_SYM_HW, that token is removed and
related code simplified.

Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Tested-by: Atish Patra <atishp@rivosinc.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Beeman Strong <beeman@rivosinc.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
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/20240416061533.921723-10-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>