[PATCH] 4/5 powerpc: Add cpufreq support for all desktop G5

This patch adds cpufreq support for all desktop "tower" G5 models. The
only G5 models still lacking cpufreq support at this point are the
Xserve and possibly the new iMac iSight (not tested). I'll have those
added soon. That patch uses the new platform functions interpreter to
implement frequency and voltage switching on most models.

Note that in order to find the low frequency value, I had to hack
something that might now work properly on all models, so if the
frequency value reported when running low speed looks bogus to you,
please report it to me. (Appart from a bogus reported value, things
should work fine).

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