Update AEM and Cortex Models versions

AEMv8-A Model release v8.2 has been made available and Trusted Firmware
has been tested against these versions as part of its CI system. This
patch updates the user guide documentation to reflect the version of AEM
and Cortex Models that Trusted Firmware has been tested against.

Also, the Linaro Release Notes link was broken and this patch updates the
link.

Change-Id: I88729cef909a69fff629036f480fd6168ad7dc9a
Signed-off-by: David Cunado <david.cunado@arm.com>