drm/i915: Move ringbuffer WAs to engine workaround list

Now that intel_engine_apply_workarounds is called on all gens, we can
use the engine workaround lists for pre-gen8 workarounds as well to be
consistent in the way we handle and dump the WAs.

v2: Ignore the sanity check of MI_MODE on Broadwater, for whatever reason
it is not sticking.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200201194004.3622493-1-chris@chris-wilson.co.uk