m68k: atari: Fix ATARI_KBD_CORE kconfig unmet dependency warning

Since the code for ATARI_KBD_CORE does not use drivers/input/keyboard/
code, just move ATARI_KBD_CORE to arch/m68k/Kconfig.machine to remove
the dependency on INPUT_KEYBOARD.

Removes this kconfig warning:

    WARNING: unmet direct dependencies detected for ATARI_KBD_CORE
      Depends on [n]: !UML && INPUT [=y] && INPUT_KEYBOARD [=n]
      Selected by [y]:
      - MOUSE_ATARI [=y] && !UML && INPUT [=y] && INPUT_MOUSE [=y] && ATARI [=y]

Fixes: c04cb856 ("m68k: Atari keyboard and mouse support.")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Suggested-by: Michael Schmitz <schmitzmic@gmail.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Link: https://lore.kernel.org/r/20210527001251.8529-1-rdunlap@infradead.org


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