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

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

These functions were forked from their Ironlake versions, so now fix
the gen checks to reflect the fact that they will only run on Haswell.

It is worth noticing that we are not considering IBX/CPT possible on
Haswell anymore. So far on Haswell enablement we kept trying to still
consider IBX/CPT as a possibility with a Haswell CPU, but this was
never tested, I really doubt it will work with the current code and we
don't really have plans to support it. Future patches will remove the
IBX/CPT code from other Haswell functions. Notice that we still have a
WARN on haswell_crtc_mode_set in case we detect non-LPT PCH.

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>