Cactus: tidy message loop and commands definitions

Creating specific header and source file for the message loop code,
separating it from the definition of test commands. Thus message loop
won't be included in tftf target.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: Ieb0c4b0bf56ed0cbbf3323cac57dd9d9b37fae92
8 files changed