Firmware: arm_scmi: add initial support for memlat vendor protocol

The memlat protocol is intended for the management of memlat based
scaling for devices like l3.

The comands in this protocol provide functionality to configure
memlat details, includes the cpugrp, memlat monitors, memlat
tunables, configuring the log levels and debugging support.

Change-Id: I1b45f833eff3aa82c3ec2c0debb703dbf8838c8a
Signed-off-by: Santosh Mardi <gsantosh@codeaurora.org>