This patch adds iomap functions to MIPS system.

Some MIPS systems are unable to define PIO space by PIO_MASK/PIO_RESERVED. 
This is the reason that I didn't use the general iomap implementation.
Signed-off-by: Yoichi Yuasa <yuasa@hh.iij4u.or.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>