Linux/m68k configuration updates
  - Unify serial console questions
  - Move serial driver config questions together
  - The Atari mouse driver depends on the Atari keyboard driver, hence on
    CONFIG_VT
  - Don't hardcode CONFIG_VT=n on VME, you may want it for a multi-machine
    kernel
  - The IRQ_* definitions are not used on Amiga, but we need them if we
    build a multi-machine kernel, too