m68k: Kill several external declarations in source files

- Replace external declarations by proper includes where availiable.
    The accesses to some symbols had to be modified, as before they were
    declared using e.g. "extern int _end", while asm-generic/sections.h uses
    e.g. "extern char _end[]"
  - Remove unused or superfluous external declarations

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

arch/m68k/atari/atakeyb.c

@@ -33,7 +33,6 @@
 #include <asm/atari_joystick.h>
 #include <asm/irq.h>
 
-extern unsigned int keymap_count;
 
 /* Hook for MIDI serial driver */
 void (*atari_MIDI_interrupt_hook) (void);