Stop irq timer for virtual vblank timer emulation if no vGPU exists,
otherwise it will keep gvt service thread busy to handle virtual vblank
but no use.
Reviewed-by: NZhi Wang <zhi.a.wang@intel.com>
Signed-off-by: NZhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: NRodrigo Vivi <rodrigo.vivi@intel.com>