msm: kgsl: convert pwrscale to use bus_mod

Use a bus specific speed flag rather than overloading
the least upper bound flag.

Change-Id: I343726e6e0d9885f39c343ed56c1667ab2008aee
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>
msm: kgsl: Don't spam the kernel log if qcom,step-pwrlevel isn't found

qcom,step-pwrlevel is a specific parameter that only applies to
certain targets.  Don't spam the world if it isn't specified.

CRs-fixed: 556418
Change-Id: Ic0dedbad65dbdcf9bc227fef4a796e22131ba68f
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
msm: kgsl: bus modifier computation

Use the vbif performance counter which counts bus busy cycles
to determine the requested bus bandwidth vote at a given
GPU frequency.

Conflicts:
        arch/arm/boot/dts/msm8974pro.dtsi

Change-Id: I18915ef8a2be75a7ef5795a6030a1f2ddd09a967
CRs-fixed: 551893
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>