tests: benchmarks/latency: limit CPU to 1 for Intel ADSP ACE4.0

Due to addition of busy threads running on other cores, and
the simulator runs in single thread bouncing through all cores,
we are wasting quite a bit of time just busy waiting. This makes
each simulator run too long for CI. So limit CPU number to 1.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>