drm/i915: Move display_mmio_offset under INTEL_INFO->display

The display register offsets are display stuff so stick
into the display portion of the device info.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220623130900.26078-4-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>