docs/platforms/rdv3: add SystemReady Compliance as supported feature

Platform RDV3 supports running SystemReady Compliance Program, thus
listing this as a supported feature by the platform.

Signed-off-by: Nuno Lopes <nuno.lopes@arm.com>
Change-Id: I35cfe25fde5ec09577df5cbd6d430b09393a86a0