perf parse-events: Fix propagation of term's no_value when cloning

perf parse-events: Fix propagation of term's no_value when cloning

The no_value field in 'struct parse_events_term' indicates that the val
variable isn't used, the case for an event name.

Cloning wasn't propagating this, making cloned event name terms
appearing to have a constant assinged to them.

Working around the bug would check for a value of 1 assigned to value,
but then this meant a user value of 1 couldn't be differentiated causing
the value to be lost in debug printing and perf list.

The change fixes the cloning and updates the "val.num ==/!= 1" tests to
use no_value instead.

To better check the no_value is set appropriately parameter comments are
added for constant values.

This found that no_value wasn't set correctly in parse_events_multi_pmu_add,
which matters now that no_value is used to indicate an event name.

Fixes: 7a6e91644708d514 ("perf parse-events: Make common term list to strbuf helper")
Fixes: 99e7138eb7897aa0 ("perf tools: Fail on using multiple bits long terms without value")
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Kan Liang <kan.liang@linux.intel.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.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>
Cc: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230831071421.2201358-4-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>