MIPS: fix __raw_* IO accessors

The purpose of the __raw* IO accessors is to provide
IO access in native-endian order. However in the current
MIPS implementation, the 16 and 32 bit variants of the
__raw accessors are swapping the values on big-endian
systems if the CONFIG_SWAP_IO_SPACE option is enabled.

The patch changes the IO accessor macros to fix this
broken behaviour.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: Daniel Schwierzeck <daniel.schwierzeck@googlemail.com>