drm/i915: remove Haswell code from ironlake_fdi_pll_enable

This function is not called on Haswell anymore.

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