m68k/atari/debug.c: possible cleanups

This patch contains the following possible cleanups:
- make the following needlessly global functions (always) static:
  - atari_mfp_console_write()
  - atari_scc_console_write()
  - atari_midi_console_write()
  - atari_init_mfp_port()
  - atari_init_scc_port()
  - atari_init_midi_port()
- #if 0 the following unused functions:
  - atari_mfp_console_wait_key()
  - atari_scc_console_wait_key()
  - atari_midi_console_wait_key()
- remove the following unused variables:
  - atari_MFP_init_done
  - atari_SCC_init_done

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>