msm: kgsl: Remove msm-dcvs pwrscale driver

The msm-dcvs pwrscale driver is no longer in development. Remove it to
avoid bitrot and simplify future target development.

Change-Id: Ic0dedbad81c2afb4bfbb377ee1a2330e115c0e71
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>