test(tc): unify platform tests traces

test(tc): unify platform tests traces

Add some traces at the start and end of platform tests. These traces
are the same regardless of the set of platform tests we run (NV
counter tests / TF-M testsuite / future set of tests).

This makes it easier to integrate these tests in the CI because we can
now have a unified "expect" script for all platform tests, instead of
having one dedicated "expect" script for each possible set of tests.

Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Change-Id: I5ec30a7a25d8a9a4a90e3338a9789acff7ad4843