drm/i915: Remove a bogus 12bpc "toggle" from intel_disable_hdmi()

The IBX 12bpc port enable toggle is only relevant when enabling
the port, not when disabling it. Also this code doesn't actually
toggle anything, and essentially just writes the port register
one extra time. Furthermore CPT/PPT don't need such workarounds
and yet we include them. Just kill it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>