drm/i915/chv: remove pre-production hardware workarounds

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[danvet: Appease gcc and remove the unused variable.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>