Revert "drm/i915: Remove i915_gem_object_get_dirty_page()"

These commits caused a regression on Lenovo t520 sandybridge
machine belonging to reporter. We are reverting them for 5.10
for other reasons, so just do it for 5.9 as well.

This reverts commit 763fedd6.

Reported-by: Harald Arnesen <harald@skogtun.org>
Signed-off-by: Dave Airlie <airied@redhat.com>