scsi: cxlflash: Support AFU interrupt mapping and registration

Add support to map and unmap the irq space and manage irq registrations with
the kernel for each allocated AFU interrupt. Also support mapping the physical
trigger page to obtain an effective address that will be provided 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>