MIPS: Loongson: Add new early_printk implmentation

This patch is based on the implementation in the lm2e-fixes branch of
Philippe's git://git.linux-cisco.org/linux-mips.git

 and the
malta-specific early_printk implementation.

Signed-off-by: Wu Zhangjin <wuzj@lemote.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>