msm: kgsl: Use the proper power level indexes

In KGSL, 0 is the index of the highest power level.
In the GMU, 0 is the index of the lowest power level.
Make the usage of indexes uniform across KGSL and only
flip them in one place before sending them to the GMU.

CRs-Fixed: 2062271
Change-Id: I356680d0cf46992418616d08c0c20cf3bf4a867e
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>
Signed-off-by: George Shen <sqiao@codeaurora.org>