iris: Create an unusable secondary aux surface

iris: Create an unusable secondary aux surface

The HIZ_CCS and MCS_CCS auxiliary surface modes require that drivers
store information about two aux buffers. We choose to represent this as
HiZ/MCS being the primary aux surface and the CCS as an secondary/extra
aux surface. This representation has the effect of placing most of the
code that will have to choose between the two aux surfaces around the
aux-map entry points.

Reviewed-by: Sagar Ghuge <sagar.ghuge@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>