It's not used on Ironlake, but is used on later generations, so make
sure it exists before we try to use it in the interrupt handlers.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Keith Packard <keithp@keithp.com>