[SCSI] ibmvscsi: Add support for capabilities MAD

Add support to ibmvscsi for the capabilities MAD. This command gets sent
to the Virtual I/O server prior to login in order to communicate client
capabilities. Additionally it returns information regarding capabilities
that the server supports. The two main capabilities communicated in this
MAD are related to partition migration and client reserve. Client reserve
allows for SCSI-2 reservations to be sent to virtual disks which are backed
by physical LUNs and will result in the reservation being sent to the
physical LUN.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>