tpm/tpm_crb: enter the low power state upon device suspend

This fix enables a platform to enter the idle state (suspend-to-idle)

The driver needs to request explicitly go_idle upon completion
from the pm suspend handler.
The runtime pm is disabled on suspend during prepare state by calling
pm_runtime_get_noresume, hence we cannot relay on runtime pm to leave
the device in low power state. Symmetrically cmdReady is called
upon resume.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Siged-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>