ivy: Introduce new test Secure Partition

In order to test multiple partitions it is needed to have at least two
different partitions with different services. This way it isn't possible
to accidentally call partition A with a service of partition B and have
it work correctly.

Cactus is meant to be the main test Secure Partition. It is the one
meant to have most of the tests that a Secure Partition has to do. Ivy
is meant to be more minimalistic. In the future, Cactus may be modified
to be a S-EL1 partition while Ivy will remain as a S-EL0 partition.

Change-Id: I29d09b9f9400b58568f9b90344a4034332a6e6e1
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>