ARM: dts: msm: update VDD_GFX CPR voltage margins for msm8996v2

Update the open-loop and closed-loop CPR voltage margin
adjustments for the VDD_GFX supply based upon the results
of hardware characterization.

Change-Id: I7b844a76ceec002147b0152f633d812d14f22ae9
Signed-off-by: David Collins <collinsd@codeaurora.org>