mips: Implement {in, out}_{le, be}_{16, 32, 64} and {in, out}_8

mips: Implement {in, out}_{le, be}_{16, 32, 64} and {in, out}_8

MIPS is the only architecture currently supported by U-Boot that does
not implement any of the in/out register access functions.

To have a interface that is useable across architectures, add the
functions to the MIPS architecture (implemented using the __raw_write
and __raw_read functions).

Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Signed-off-by: Mario Six <mario.six@gdsys.cc>