sched: Add snapshot of Window Assisted Load Tracking (WALT)

This snapshot is taken from msm-4.9 as of commit 935c3e96d14c14d
(Revert "sched/fair: Limit sync wakeup bias to waker cpu").

Change-Id: I53b79289b37b7a352ae2a04b03cdadb3f2e564c6
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
[satyap@codeaurora.org:
1. Resolve merge conflicts
2. Fix indentation issues
3. Fix compilation issues for ARCH=um & SDM855
4. Comment out parts of code for compilation
5. Remove stubs introduced by commit: d8e3774e
(cpufreq: Various changes to allow sugov to compile)]
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>