ci: Improve FIH job result assesment

Modify the FIH CI job to fail in case successful boot happens
below a certain treshold. CI should fail if a successful boot
is achieved by bypassing one or two instructions as it would
defeat the purpose of the FIH mechanisms.

Signed-off-by: Roland Mikhel <roland.mikhel@arm.com>
Change-Id: If1703d57e3ba87e5fd73d4ba954bfd38ed1c0cc6