drm/i915: Don't save/restore hardware status page address register

It's cleaned before saving and re-initialized after restoring.
So don't need to save/restore it. And also new chip has new address
for hardware status page register, don't write to old address.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>