Update the supported boards script and list
    
    Update the supported boards list and script to be more
    up to date and better reflect the aarch64 platforms we
    actively support.
    
    Also clarify in the help what supported in this context
    actually means as we at times get equiries assuming it
    means the device is fully supported in Fedora so clarify
    that the support in this context is purely about writing
    out the early boot firmware.
    
    Signed-off-by: Peter Robinson <pbrobinson@gmail.com>