agp/intel: support for new chip variant of IGDNG mobile

New variant of IGDNG mobile chip has new host bridge id.

[anholt: Note that this new PCI ID doesn't impact the DRM, which doesn't
care about the PCI ID of the bridge]

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>