drm/i915: gen7: Implement an L3 caching workaround.

commit e4e0c058a19c41150d12ad2d3023b3cf09c5de67 upstream.

This adds two cache-related workarounds for Ivy Bridge which can lead to
3D ring hangs and corruptions.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=41353
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=44610
Tested-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>