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.