sst: avoid unnecessary firmware reloading for MRST

SST HW on MRST doesn't need to reload the firmware during suspend/resume
cycle, so remove the extra workload. This also fix a bug that the firmware
sample rate can't be modified when there is no active playback/capture
stream.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>