MIPS: Octeon: Reverse the order of register accesses to the FAU

64 bit access is unaffected but for 32 bit access, swap high and
low words.  Similarly for 16 bit access, reverse the order of the
four possible words, and for 8 bit access reverse the order of byte
accesses.

Signed-off-by: Paul Martin <paul.martin@codethink.co.uk>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9630/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>