test(notifications): validate SRI is delayed

This test aims at validating that when flag to delay SRI is set,
effectively the SWd is not preempted upon a call to the interface
FFA_NOTIFICATION_SET.
Leveraging the commits [1] and [2], the cactus SP that is setting the
notifications is also sending an echo test command to another SP.
With the help of [2], TFTF can request the counting of test commands
to the echo destination prior and after the setting of notifications,
evaluating that before execution returning to TFTF the counting has
been incremented.

[1] https://review.trustedfirmware.org/c/TF-A/tf-a-tests/+/11596/36
[2] https://review.trustedfirmware.org/c/TF-A/tf-a-tests/+/11595/36

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: If343db29517ad64533e98bc6fab5127283ffbf94
2 files changed