MIPS: Lemote 2F: Add NAS support

Kernel support for this machine is almost the same as Fuloong 2F; the only
difference is that it uses the serial port provided by Loongson 2F processor
as Yeeloong 2F does.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/656/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>