scsi-disk: move all non-DMA commands to scsi_disk_emulate_command

scsi-disk: move all non-DMA commands to scsi_disk_emulate_command

We want to use separate SCSIReqOps for emulated commands needing an
allocated buffer vs. those that are zerocopy when the HBA supports
S/G lists.  Ensure that all of the former are in scsi_disk_emulate_command.

Commands that do not have any parameters are more similar to emulated
commands, so also move them, even if they do I/O.

Finally, MODE SELECT and MODE SELECT(10) are broken because we do not
yet support passing parameter data _to_ emulated commands, so disable
them.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>