[SCSI] ibmvfc: Add flush on halt support

The virtual I/O server controlling the NPIV adapter associated with
a virtual fibre channel adapter can send a HALT event to the client.
When this occurs, the client can no longer send commands until a RESUME
is received. By adding support for flush on halt, we will get all of
our outstanding commands flushed back before the Virtual I/O server
enters the halt state, eliminating potential command timeouts for
outstanding commands which might occur if we did not support this feature.

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