Stop gvt scheduler timer if no vGPU exists, otherwise it keeps
gvt service thread busy to handle request schedule event but no
actual schedule activity required.
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>