arm-bsp/corstone700-test-app: adding test recipe for systems comms

This commit provides a recipe that generates a Linux userspace
application used for testing the communication between Corstone700 cores.

Change-Id: I7c00653b0fcd6d9074510bbb70a838762aed0150
Signed-off-by: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>