defconfig: arm64: msm: enable mem-acc-regulator driver

Enable mem-acc-regulator driver on arm64 targets. It will initially be
used on MSM8916 board so that memory accelerator can control the memory
access delay when switching corners.

Change-Id: I9746509ed59b62ee8b1a800e2942a07bedf866d7
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>