mips: io.h: Add defines for read/write/in/out functions

Add defines for {read,write}{b,w,l,q}(), {read,write}s{b,w,l,q}() and
{in,out}s{b,w,l,q}() functions to make asm-generic/io.h aware of them.

Signed-off-by: Igor Prusov <ivprusov@salutedevices.com>