regulator: mem-acc-regulator: Add support for the new scm_call2 API

The scm library has added support for a new secure world
interface that is more aligned to the ARMv8 SMC calling
convention. Use the new API while maintaining backward
compatibility.

Change-Id: Ia6e5ab948f31c03cfcf7d1391154c18148b7099f
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>