m68k: Merge mmu and non-mmu versions of sys_call_table

Impact for nommu:
  - Store table in .rodata instead of .text,
  - Let kernel/sys_ni.c handle the stubbing of MMU-only syscalls,
  - Implement sys_mremap and sys_nfsservct,
  - Remove unused padding at the end of the table.

Impact for mmu:
  - Store table in .rodata instead of .data.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Greg Ungerer <gerg@uclinux.org>