[POWERPC] Fix IDE build with ARCH=ppc

The recent IO accessor changes broke IDE on arch/ppc due to the IDE
stream IO macros using the new reads/writes{b,w,l} accessors that
are only defined for arch/powerpc. This adds them to arch/ppc.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>