- Fix compile error when accessing `process_subcommands_now_P`.
- Use `const` var eliminating double-negative (to make code more understandable).

Replaced `PID_MAX` with `BANG_MAX` since it should be the correct define to be used when PID is not enabled.

Incomplete.

See https://www.patreon.com/posts/creality-cr10-24602624

Apply minimum `C` in `M303`. `PID_autotune()` needs to be called with a 'C'ycles-parameter >2 to give meaningful (different from 0) PID-factors. Therefore silently raise C to 3. Fixing one aspect of #13104

add MMU2