perf cs-etm: Add separate decode paths for timeless and per-thread modes

Timeless and per-thread are orthogonal concepts that are currently
treated as if they are the same (per-thread == timeless). This breaks
when you modify the command line or itrace options to something that the
current logic doesn't expect.

For example:

  # Force timeless with Z
  --itrace=Zi10i

  # Or inconsistent record options
  -e cs_etm/timestamp=1/ --per-thread

Adding Z for decoding in per-cpu mode is particularly bad because in
per-thread mode trace channel IDs are discarded and all assumed to be 0,
which would mix trace from different CPUs in per-cpu mode.

Although the results might not be perfect in all scenarios, if the user
requests no timestamps, it should still be possible to decode in either
mode. Especially if the relative times of samples in different processes
aren't interesting, quite a bit of space can be saved by turning off
timestamps in per-cpu mode.

Signed-off-by: James Clark <james.clark@arm.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Denis Nikitin <denik@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.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: Peter Zijlstra <peterz@infradead.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20230424134748.228137-8-james.clark@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>