scsi: cxlflash: Support AFU interrupt management

Add support to allocate and free AFU interrupts using the OCXL provider
services. The trigger page returned upon successful allocation will be mapped
and exposed to the cxlflash core in a future commit.

Signed-off-by: Uma Krishnan <ukrishn@linux.vnet.ibm.com>
Acked-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>