cpufreq: pmac64: provide cpufreq transition latency for older G5 models

Currently cpufreq ondemand governor cannot used on older G5 models,
because the transition latency is set to CPUFREQ_ETERNAL. Provide a
value based on a measurement on Xserve G5, which happens to be also the
highest allowed latency.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>