BACKPORT: cpufreq: schedutil: Use policy-dependent transition delays

Make the schedutil governor take the initial (default) value of the
rate_limit_us sysfs attribute from the (new) transition_delay_us
policy parameter (to be set by the scaling driver).

That will allow scaling drivers to make schedutil use smaller default
values of rate_limit_us and reduce the default average time interval
between consecutive frequency changes.

Make intel_pstate set transition_delay_us to 500.

BACKPORT: Modified to support the separate up_rate_limit_us and
down_rate_limit_us (upstream just has a single rate_limit_us). Also
dropped the changes for intel_pstate as there's a merge conflict.

Change-Id: I62a8543879a4d8582cdcb31ebd55607705d1c8b1
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
(cherry picked from commit 1b72e7fd304639f1cd49d1e11955c4974936d88c)
Signed-off-by: Brendan Jackman <brendan.jackman@arm.com>