drm/i915: Skip clock checks on BDW

We don't have clock state readout support for DDI, so skip the pipe
config clock checks on all DDI platforms.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>