cpufreq: arm_big_little: add in-kernel switching (IKS) support

This patch adds IKS (In Kernel Switcher) support to cpufreq driver.

This creates a combined freq table for A7-A15 CPU pairs. A7 frequencies
are virtualized and scaled down to half the actual frequencies to
approximate a linear scale across the combined A7+A15 range. When the
requested frequency change crosses the A7-A15 boundary a cluster switch
is invoked.

Based on earlier work from Sudeep KarkadaNagesha.

Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>