m68k/serial: Remove references to obsolete serial config options

  - ATARI_MFPSER, ATARI_MIDI, MULTIFACE_III_TTY, and DN_SERIAL
    have no corresponding drivers (anymore),
  - Clean up SERIAL_CONSOLE dependencies and help text.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

diff --cc arch/m68k/Kconfig.devices
Simple merge

diff --cc arch/m68k/configs/amiga_defconfig
Simple merge

diff --cc arch/m68k/configs/apollo_defconfig
Simple merge

diff --cc arch/m68k/configs/atari_defconfig
Simple merge

diff --cc arch/m68k/configs/multi_defconfig
Simple merge

diff --cc arch/m68k/configs/mvme16x_defconfig
Simple merge