msm: kgsl: Disable POPP feature

POPP feature attempts to push the GPU frequency down if it detects a
stable run at particular frequency. However it caused performance drop.
Disable the feature to avoid performance regression.

Change-Id: I0ebfc98cdf626199bada7fbf7a3b67792bbf160c
Signed-off-by: George Shen <sqiao@codeaurora.org>