sst: Change the SST driver PCM interface

The PCM interface in SST driver is cmds only, this patch changes the interface to open, close and cmd interface.
This allows SST driver to keep easy track of handles open

Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>