qemuBuildControllerDevStr: Split out formatting of SCSI controller
Move the code into a new function called qemuBuildControllerSCSIDevStr
so that the code is self contained and the original function easier to
follow.
This patch also moves the formatting of the properties relevant only for
the 'virtio-scsi' controller to the specific case so it's more clear
where they belong to.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>