cpufreq: Various changes to allow sugov to compile

Until various scheduler components are merged, our modified sugov cannot
compile due to dependencies on WALT.  Introduce the necessary stubs to
provide compilation.

Change-Id: I11e37ecaf5bf7eae2068bb9bb3d535e2d5571543
Signed-off-by: Jonathan Avila <avilaj@codeaurora.org>