drm/i915/kbl: Add WaDisableFenceDestinationToSLM for A0

Add this workaround for kbl revid A0 only.

v2: rebase
v3: carve out a non related workaround (Chris)

References: HSD#1911714
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1465309159-30531-9-git-send-email-mika.kuoppala@intel.com