MLECO-4732: Updating FVP version

Dockerfile updated for it to download the latest Fixed Virtual
Platform (FVP) version 11.24.

Minor documentation change to say that Arm Corstone-310 FVP is
also available to download from the Arm Ecosystem FVP page.

Change-Id: Icd19f71f53b4a6f1b912919e42e941fb23800d57
Signed-off-by: Kshitij Sisodia <kshitij.sisodia@arm.com>