intel/l3: Allow platforms to have no l3 configurations

intel/l3: Allow platforms to have no l3 configurations

On some gen12 platforms we will use the L3FullWayAllocationEnable and
never reconfigure the L3 setup.

Suggested-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4956>