stex: Add S3/S4 support

Add S3/S4 support, add .suspend and .resume function in pci_driver.  In
.suspend handler, driver send S3/S4 signal to the device.

Signed-off-by: Charles Chiou <charles.chiou@tw.promise.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>