Update Foundation, AEM and Cortex Models versions

Update Foundation, AEM and Cortex Models versions

Trusted Firmware has been tested as part of its CI system against Cortex
and Foundation models in the 11.1 Model release available on
developer.arm.com. Trusted Firmware has also been tested against the
v8.7 AEM model.  This patch updates the user guide documentation to
reflect the version of the Foundation, AEM and Cortex Models that
Trusted Firmware has been tested against.

Change-Id: Ia0f51469032427b6056567d151bf8144a7cf0e42
Signed-off-by: Eleanor Bonnici <Eleanor.bonnici@arm.com>