scsi: move sense handling to generic code

scsi: move sense handling to generic code

With this patch, sense data is stored in the generic data structures
for SCSI devices and requests.  The SCSI layer takes care of storing
sense data in the SCSIDevice for the subsequent REQUEST SENSE command.

At the same time, get_sense is removed and scsi_req_get_sense can use
an entirely generic implementation.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>