[PATCH] ppc64: Big-endian I/O memory accessors.

I/O memory accessors. Big-endian version. For those busses/devices
that do export big-endian I/O memory.

Of notable relevance/reference:

   http://lwn.net/Articles/132804/
   http://ozlabs.org/pipermail/linuxppc-embedded/2005-August/019798.html
   http://ozlabs.org/pipermail/linuxppc-embedded/2005-August/019752.html

Signed-Off-By: Arthur Othieno <a.othieno@bluewin.ch>
Signed-off-by: Paul Mackerras <paulus@samba.org>