drm/i915: fix checks inside ironlake_crtc_{enable, disable}

The last commit forked a Haswell version, so now we remove Haswell
code from these functions.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>