drm/i915: Remove pre-production Broxton register workarounds

We've begun excluding pre-production Broxton machines since commit
0102ba1f ("drm/i915: Add early BXT sdv to the list of preproduction
machines"), now remove the list of workaround register values for those
early machines.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20170927093325.24206-1-chris@chris-wilson.co.uk


Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171114134340.5439-1-chris@chris-wilson.co.uk