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/mvme16x/config.c

@@ -48,7 +48,6 @@ extern unsigned long mvme16x_gettimeoffset (void);
 extern int mvme16x_hwclk (int, struct rtc_time *);
 extern int mvme16x_set_clock_mmss (unsigned long);
 extern void mvme16x_reset (void);
-extern void mvme16x_waitbut(void);
 
 int bcd2int (unsigned char b);