ARM: dts: msm: Add GPU power level speed bin for SDM670

This change adds a new speedbin to limit the GPU freq to 430MHZ on
some SKUs.

Change-Id: I8a7cecfc4baed24f45ecf84c92a4afc0f705634b
Signed-off-by: Akhil P Oommen <akhilpo@codeaurora.org>