feat(cactus): count requests received

Message loop counts the amount of requests received in each core. The
counting can be accessed through newly added test command
CACTUS_GET_REQ_COUNT_CMD.
Added such special command to be able to test delay Schedule Receiver
Interrupt, in the context of the notifications feature.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: Id0a5a9cf58e10d1221a1a0f0af6264474fe7e020
3 files changed