scsi: cxlflash: Support adapter file descriptors for OCXL

Allocate a file descriptor for an adapter context when requested. In order to
allocate inodes for the file descriptors, a pseudo filesystem is created and
used.

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>