feat(tsp): enable test cases for EL3 SPMC

Introduce initial test cases to the TSP which are
designed to be exercised by the FF-A Test Driver
in the Normal World. These have been designed to
test basic functionality of the EL3 SPMC.

These tests currently ensure the following functionality:
  - Partition discovery.
  - Direct messaging.
  - Communication with a Logical SP.
  - Memory Sharing and Lending ABIs
  - Sharing of contiguous and non-contiguous memory regions.
  - Memory region descriptors spread of over multiple
    invocations.

Signed-off-by: Marc Bonnici <marc.bonnici@arm.com>
Signed-off-by: Shruti Gupta <shruti.gupta@arm.com>
Change-Id: Iaee4180aa18d6b7ac7b53685c6589f0ab306e876