ARM: dts: msm: Add GFX CPR device configuration for sdm660

GPU subsystem in sdm660 is supplied by either LDO300(VDD_GFX) in
LDO mode or VDD_CX in BHS mode. This LDO300 is CPR managed and supports
CPR closed-loop operation. Add CPR device node with required configuration
for supporting CPR closed-loop operation for sdm660.

CRs-Fixed: 1068294
Change-Id: Id12a50563f6cef196ef76816fcf8e177b9a3fa97
Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org>