Revert "drm/i915: Include display_mmio_offset in sequencer index/data registers"

We use port I/O for VGA register access, so adding display_mmio_offset
is just wrong.

This reverts commit 56a12a50.

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