nrd/rdv3: SCMI module to bind back to SCP platform module

When SCP platform module binds to SCMI module, SCMI module will try to
bind back to platform  module. Add support for the bind back APIs.

The current implementation of RSE do not support SCMI. This patch can be
removed once SCMI support is enabled in RSE. In that scenario, RSE will
subscribe to the system power-down notifications, which will then be
handled directly by the SCP SCMI module.

Change-Id: Ib41a414f29797c9e9d7c5bade56f5f4cb6403c24
Signed-off-by: Pranav Madhu <pranav.madhu@arm.com>