TFTF: trigger direct messaging between SPs

Use cactus command 'CACTUS_REQ_ECHO_SEND_CMD' to make cactus SPs
communicate with each other using direct message interfaces.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: Idc266cfb8b5661d1b2386d20a2758489f8ac894e
2 files changed