drm/i915: Unconditionally apply the Broxton register workaround set

Having removed the preproduction Broxton support (see commit 0102ba1f
("drm/i915: Add early BXT sdv to the list of preproduction machines")),
we know we then always need the production Broxton workaround set and do
not need a predicate upon revision.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171114134340.5439-2-chris@chris-wilson.co.uk