perf expr: Allow NaN to be a valid number

perf expr: Allow NaN to be a valid number

Currently only floating point numbers can be parsed, add a special
case for NaN.

Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: James Clark <james.clark@arm.com>
Cc: Kaige Ye <ye@kaige.org>
Cc: John Garry <john.g.garry@oracle.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240209204947.3873294-2-irogers@google.com