chore(docs): update supported FVP models doc

Update supported models list according to changes for v2.6 release in
ci/tf-a-ci-scripts repository:
* general FVP model update: d10c1b9
* gic600 update: aa2548a
* CSS prebults model update: f1c3a4f

Signed-off-by: Maksims Svecovs <maksims.svecovs@arm.com>
Change-Id: If2841f05238facb3cace7d5c8a78083d54f35e27
1 file changed