VFIO region space is allocated when one region is registered for
one vgpu. So free the space when destroy the vgpu.

Also change the parameter of detach_vgpu callback to use vgpu directly.

Fixes: b851adea ("drm/i915/gvt: Add opregion support")
Reviewed-by: NZhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: NHang Yuan <hang.yuan@linux.intel.com>
Signed-off-by: NZhenyu Wang <zhenyuw@linux.intel.com>