scsi: cxlflash: Support adapter context mmap and release

The cxlflash userspace API requires that users be able to mmap and release the
adapter context. Support mapping by implementing the AFU mmap fop to map the
context MMIO space and install the corresponding page table entry upon page
fault. Similarly, implement the AFU release fop to terminate and clean up the
context when invoked.

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>