drm/etnaviv: update gc7000 chip identity entry

Use ~0U as marker for 'I do not care'. I am not sure what
GC7000 based devices are in the wild and I do not want to
break them. In the near future we should extend the hwdb.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>