ARM: dts: msm: add a mem-acc-regulator device for msm8939

The memory accelerator controls delays while accessing memories, the
delays should be changed according to CPR corner switching.

Add a mem-acc-regulator device node and assign it to mem-acc-supply
property in CPR device node. This make sure that the memory accelerator
can be controlled while changing corners.

Change-Id: If5eb70b4bd78d51c458c4923b6711ea3ae75802f
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>