iris: Make mocs an inline helper in iris_resource.h

iris: Make mocs an inline helper in iris_resource.h

Now that it uses ISL rather than genxml code, there's no need for it to
live as a vtable function inside the state module.  We can just make it
a static inline helper in iris_resource.h so it's available throughout
the codebase.

Fixes: a4da6008b6a ("iris: Use mocs from isl_dev.")
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3720>