boards: intel_adsp_cavs18: add test coverage

Increase the test coverage for intel_adsp_cavs18. To keep its
test coverage as the same as cavs15 and cavs25.

Currently only one test sutite failed , See #42157.
with #42158 expend the time of ringbuffer testing, it can reach
100% pass rate.

Signed-off-by: Enjia Mai <enjia.mai@intel.com>