regulator: mem-acc-regulator: Add a driver to control the MEM ACC

The memory accelerator (MEM ACC) controls the delays applied during
memory access. These delays vary based on the power-mode (corner)
on which the memory is connected. This driver adds a regulator
interface to configure the power-mode of the memory accelerator
based on the APC (application processor) corner.

Change-Id: I830ff000f8a16c4d3de5bdebf48d424354ddb086
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>