powerpc: Expose PMCs & cache topology in sysfs on 32-bit

The file arch/powerpc/kernel/sysfs.c is currently only compiled for
64-bit kernels.  It contain code to register CPU sysdevs in sysfs and
add various properties such as cache topology and raw access by root
to performance monitor counters (PMCs).  A lot of that can be re-used
as is on 32-bits.

This makes the file be built for both, with appropriate ifdef'ing
for the few bits that are really 64-bit specific, and adds some
support for the raw PMCs for 75x and 74xx processors.

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