ARM: dts: msm: specify dynamic VDD_GFX CPR floor voltages for msm8996v2

Specify a maximum floor to ceiling voltage range for each VDD_GFX
corner.  Also reduce the fixed floor voltages to 520 mV in order
to allow CPR closed-loop voltages to settle lower.  This results
in power savings.

Change-Id: If4988e17ae57c798b068ebd6706aeeba793e1814
Signed-off-by: David Collins <collinsd@codeaurora.org>