feat(realm): assign MECID when creating realms

This change allows TFTF to assign a MECID to every realm that is
created by passing an extra parameter to the Realm creation helpers.

Signed-off-by: Juan Pablo Conde <juanpablo.conde@arm.com>
Change-Id: I89bf08011eb005d949a195b406b073955f23f5ad
17 files changed