drm/i915/gvt: Select appropriate mmio list at initialization time

Select appropriate mmio list at initialization time, so we don't need to
do duplicated work at where requires the mmio list.

V2:
  - Add a termination mark of mmio list.

Signed-off-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>