infra/platforms: update fvp download section

The Neoverse reference design FVPs are now available for download from
the Arm FVP ecosystem page. Update the section on platform FVP download
with this information for all the supported platforms.

Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: I3f7e7d7dc0a20684140d5be61a531700fba56120