inline to fix warnings, smaller build size (sometimes)

[thinkyhead]

Background: The compiler complains because functions declared static in a shared header are only defined in one compilation unit (Marlin_main.cpp). This is easy to fix, but it would be nice if we could use static for the size reduction is produces as a side-effect.

• Default config:
  • 52,426 without static or inline
  • 51,930 with static or inline – saves 496 bytes ?!
• With NOZZLE_CLEAN (calling these functions from 2 code units):
  • 53,854 without static or inline
  • 53,854 with inline
  • 53,618 with static – saves 236 bytes ?!