drm/i915/kbl: Add WaForGAMHang

Add this workaround for A0 and B0 revisions

References: HSD#2226935
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1465309159-30531-19-git-send-email-mika.kuoppala@intel.com