x86_64: Quieten Atari keyboard warnings in Kconfig

Not directly related to x86, but I got tired of seeing these warnings on every
kconfig update when building on a non m68k box:

drivers/input/keyboard/Kconfig:170:warning: 'select' used by config symbol 'KEYBOARD_ATARI' refers to undefined symbol 'ATARI_KBD_CORE'
drivers/input/mouse/Kconfig:182:warning: 'select' used by config symbol 'MOUSE_ATARI' refers to undefined symbol 'ATARI_KBD_CORE'

I moved the definition of ATARI_KBD_CORE into drivers/input/keyboard/Kconfig
so it's always seen by Kconfig.

Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>