cpufreq: Add a notifer chain that governors can use to report information

Some modules can benefit from getting additional information cpufreq
governors use to make frequency switch decisions.
This change lays down a basic framework that the governors can use
to report additional information (Eg: CPU's load) information to
the clients that subscribe to cpufreq govinfo notifier chain.

Change-Id: I511b4bdb7d12394a31ce5352ae47553861e49303
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>

Original commit: https://bitbucket.org/arter97/android_kernel_samsung_exynos7420/commits/24eb648e02309b1376f7d297530eb9662f9b63f1