drm/xe/xe2: Add missing mocs entry

Add index 4 so WB on both L3 and L4 can be used by userspace.

Bspec: 71582
Link: https://lore.kernel.org/all/7oqovb356dx2hm5muop3xjqr4kv7m5fzjisch3vmsmxm33ygtv@eib4jielia35/


Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20231004150317.3473731-1-lucas.demarchi@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>