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/sun3x/config.c

@@ -23,7 +23,6 @@
 #include "time.h"
 
 volatile char *clock_va;
-extern volatile unsigned char *sun3_intreg;
 
 extern void sun3_get_model(char *model);