drm/i915/bdw: Don't wait for c0 threads on forcewake

It's no longer a required workaround on BDW.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
[danvet: Move compile fix from a later patch to this one.]
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>