Add a few more test cases in FWU group

Added a few more test cases in FWU group to authenticate the images
involved in the FWU process (ns_bl2u, scp_bl2u and bl2u) using RSA
3k and 4k certificate key.

Change-Id: Icfa503c98ed3c5222c9e79c205c5661f62293caa
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
6 files changed