cpufreq: Make down_differential parameter configurable.

The down_differential parameter determines the down threshold for
the governor to scale down the frequency and when made configurable
provides for a variable operating range for the governor.

Usage:
cat /sys/devices/system/cpu/cpu0/cpufreq/ondemand/down_differential
echo 30 >
/sys/devices/system/cpu/cpu0/cpufreq/ondemand/down_differential

Change-Id: Ice94b8ae961aa3df7f9582c2af2275414931faed
Signed-off-by: Brian Steuer <bsteuer@codeaurora.org>
ondemand: Add support to consider other cpu load when scaling frequencies

Currently only current cpu load is considered when frequency scaling.
As a side effect of this when scheduler migrates a thread to a slower
core, the execution time increases unexpectedly.

The new algorithm not only considers current cpu load for frequency
scaling, but also takes into account load of other online cpus. The
treshold for this can be controlled using up_threshold_any_cpu_load.
When the up_threshold_any_cpu_load is crossed in any cpu then the
current cpu is set to sync_freq.

Also, when more than one cpu is online a two step ramp-up mechanism
is used. When the up_threshold_multi_core is crossed the cpu is ramped
up to optimal_freq which is less than policy->max and set to a power
friendly value.

Change-Id: I64bed1b142cde1f239e73aa1f78981c78aaf59ce
Signed-off-by: Narayanan Gopalakrishnan <nargop@codeaurora.org>

Conflicts:
	drivers/cpufreq/cpufreq_ondemand.c