scsi: ibmvfc: Add size parameter to ibmvfc_init_event_pool()

With the upcoming addition of Sub-CRQs the event pool size may vary
per-queue.

Add a size parameter to ibmvfc_init_event_pool() such that different size
event pools can be requested by ibmvfc_alloc_queue().

Link: https://lore.kernel.org/r/20210114203148.246656-5-tyreld@linux.ibm.com
Reviewed-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>