[PATCH] pmac: fix cpufreq for old tipb 550Mhz

The old 550Mhz titanium powerbook can switch to a lower frequency
(500Mhz). A user has been repeately reporting overtemp conditions on his
machine at high speed so this simple patch adds support to PowerMac
cpufreq for this machine. The difference in frequency isn't big but seem
enough to fix that user's problems. The patch has been around for some
time now and doesn't seem to cause any problem, so I suppose it could go
in now.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Alain RICHARD <alain.richard@equation.fr>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>