Firmware: arm_scmi: initial support for plh vendor protocol

The perf lock hardening protocol is intended for the management
of perf lock hardening on RIMPS.
The commands in this protocol provide functionality to configure
plh details, plh tunables, configuring the log levels and
debugging support.

Change-Id: I9f5292ee3e32a038160e66d38ec15637a55458fd
Signed-off-by: Gaurav Singh <sgaurav@codeaurora.org>