docs: add FFA_MSG_SEND_DIRECT_REQ2/RESP2 support

Add FFA_MSG_SEND_DIRECT_REQ2/RESP2 to list of supported
interfaces. Also update references to FFA_MSG_SEND_DIRECT_REQ
that also apply to FFA_MSG_SEND_DIRECT_REQ2.

Signed-off-by: Kathleen Capella <kathleen.capella@arm.com>
Change-Id: I72271019381a8eaff1a8ecdb4580f89e984f4d48
diff --git a/docs/threat_model_spm.rst b/docs/threat_model_spm.rst
index d0b16da..fffe87c 100644
--- a/docs/threat_model_spm.rst
+++ b/docs/threat_model_spm.rst
@@ -893,10 +893,11 @@
 |                        | SPMC and SPs, potentially leading to illegal state |
 |                        | transitions and deadlocks.**                       |
 |                        | An endpoint can call into another endpoint         |
-|                        | execution context using FFA_MSG_SEND_DIRECT_REQ    |
-|                        | ABI to create a call chain. A malicious endpoint   |
-|                        | could abuse this to form loops in a call chain that|
-|                        | could lead to potential deadlocks.                 |
+|                        | execution context using FFA_MSG_SEND_DIRECT_REQ (or|
+|                        | FFA_MSG_SEND_DIRECT_REQ2) ABI to create a call     |
+|                        | chain. A malicious endpoint could abuse this to    |
+|                        | form loops in a call chain that could lead to      |
+|                        | potential deadlocks.                               |
 +------------------------+----------------------------------------------------+
 | ``Diagram Elements``   | DF1, DF2, DF4                                      |
 +------------------------+----------------------------------------------------+