Merge changes from topic "scmi-msg" into integration

* changes:
doc: maintainers: add scmi server
drivers: move scmi-msg out of st

drivers: move scmi-msg out of st

Make the scmi-msg driver reused by others.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Change-Id: I5bc35fd4dab70f45c09b8aab65af4209cf23b124