ARM: dts: msm: Add VDD_GFX mem-acc regulator device for msm8996

Add a mem-acc supply regulator to the VDD_GFX CPR3 controller
device node in order to enable control of memory settings when
the VDD_GFX supply is scaled. Define the appropriate VDD_GFX
CPR3 regulator to VDD_GFX mem-acc regulator corner mappings
depending upon the hardware revision.

Change-Id: Ie3553518cbd79f3099da465c5732aab89c3aa872
Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>