drm/i915: rip out pre-DDI stuff from haswell_crtc_mode_set

Especially getting rid of all things lvds is ... great!

v2: Drop the two additional pre-hsw hunks noticed by Paulo Zanoni.

v3:
- handle DP ports correctly (spoted by Paulo)
- don't leave {} behind for a single-line block (again spotted by
  Paulo)
- kill another if (IBX || CPT) block

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