scsi: cxlflash: Separate AFU internal command handling from AFU sync specifics

To date the only supported internal AFU command is AFU sync. The logic
to send an internal AFU command is embedded in the specific AFU sync
handler and would need to be duplicated for new internal AFU commands.

In order to support new internal AFU commands, separate code that is
common for AFU internal commands into a generic transmission routine
and support passing back command status through an IOASA structure.
The first user of this new routine is the existing AFU sync command.
As a cleanup, use a descriptive name for the AFU sync command instead
of a magic number.

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