tpm: selftest: add test covering async mode

Add a test that sends a tpm cmd in an async mode.
Currently there is a gap in test coverage with regards
to this functionality.

Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>