ARM: dts: msm: Adjust VDD_GFX CPR margins for msm8996v2

Adjust the open and closed loop voltage margins for the Graphics
voltage rail to match updated silicon characterization data. Note
that without runtime calculation of floor voltages, potential
power savings may be limited by the predefined floor voltages that
are treated as hard limits.

Change-Id: I802b33e6f418264accb38ea11d819aa1bed56490
Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>