[SCSI] pmcraid: support SMI-S object model of storage pool

PMC-Sierra mgmt application uses SMI-S model. According to SMI-S, the
object model exposed by the SMI-S provider should show an StoragePool
which contains member disks of a RAID Virtual disk and StorageVolume
based on the StoragePool. But according to SMI-S, there is a possibility
where StoragePool is created but StorageVolume is not yet created. To
satisfy this scenario, we are trying a hidden RAID Virtual disk. The
hidden RAID virtual disk will not be exposed to OS. Once a StorageVolume
is created for this RAID virtual disk it is exposed.

Signed-off-by: Anil Ravindranath<anil_ravindranath@pmc-sierra.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>