intel/disasm: Don't rely on FALLTHROUGHTs to print unsupported SFID

intel/disasm: Don't rely on FALLTHROUGHTs to print unsupported SFID

The code works but is a bit fragile if we ever add a case that has a
less strict requirement (a smaller gen) than the case above.  To avoid
having to reason about this, refactor code to use a variable to
indicate whether the SFID is supported or not.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Marcin Ślusarz <marcin.slusarz@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7742>