add test application for testing features in corstone700

this test application currently tests

1. Host to Boot processor communication through Non secure MHU
2. Host timer interrupts reaching boot processor through
   interupt router and interrupt collator

Change-Id: I8435e27fefdebcdc30e4a9e5e022450abbaeb0a5
Signed-off-by: Morten Borup Petersen <morten.petersen@arm.com>