drm/i915: Add display_display_mmio_offset to intel_device_info

Add an optional offset to intel_device_info, which will added
to most display register offsets.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -337,6 +337,7 @@ struct drm_i915_gt_funcs {
 	DEV_INFO_FLAG(has_llc)
 
 struct intel_device_info {
+	u32 display_mmio_offset;
 	u8 gen;
 	u8 is_mobile:1;
 	u8 is_i85x:1;