[SCSI] ibmvfc: Add support for NPIV Logout

This patch adds support for a new command supported by the Virtual I/O
Server, NPIV Logout. The command will abort all outstanding commands
and log out of the fabric. Currently, the only way to do this is
by breaking the CRQ, which can take a fairly long time when lots of
commands are outstanding. The NPIV Logout commands provides a mechanism
to accomplish virtually the same function, but is much faster.

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