TFTF: helpers for SPM tests

Added functions and macros to help check at the beginning of the test,
that system is as expected for SPM tests in which Hafnium is deployed as
SPMC.
This includes:
- Checking SPMC has expected FFA_VERSION;
- Checking that expected FF-A endpoints are deployed in the system;
- Getting global TFTF mailbox.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: I9195bcff8ed93156e838b192bb70a9634e18fbbf
4 files changed