scsi: ibmvfc: Make discovery buffer per protocol channel group

scsi: ibmvfc: Make discovery buffer per protocol channel group

The target discovery buffer that the VIOS populates with targets is
currently a host adapter field. To facilitate the discovery of NVMe targets
as well as SCSI another discovery buffer is required. Move the discovery
buffer out of the host struct and into the ibmvfc_channels struct so that
each channels instance for a given protocol has its own discovery buffer.

Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Link: https://lore.kernel.org/r/20230921225435.3537728-11-tyreld@linux.ibm.com
Reviewed-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>