- Remove several outdated comments
- Clearify the definition of zimage_start and zimage_size and the their
  usage

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1382/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>