[SCSI] libosd: OSD Security processing stubs

Layout the signing of OSD's CDB and all-data security modes. The actual
code for signing the data and CDB is missing, but the code flow and the extra
buffer segments are all in place.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Reviewed-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>