qemuDomainControllerIsBusy: Fully populate switch statement

qemuDomainControllerIsBusy: Fully populate switch statement

Typecast the controller type variable to the appropriate type and add
the missing controller types for future extension.

Note that we currently allow only unplug of
VIR_DOMAIN_CONTROLLER_TYPE_SCSI thus the other controller types which
are not implemented return false now.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>