docs(spm): add threat model for el3 spmc

Threat model for EL3 SPMC.
The mitigations are based on the guidance
provided in FF-A v1.1 EAC0 spec.

Signed-off-by: Shruti Gupta <shruti.gupta@arm.com>
Change-Id: I7f4c9370b6eefe6d1a7d1afac27e8b3a7b476072
diff --git a/docs/glossary.rst b/docs/glossary.rst
index aeeb133..e2cc794 100644
--- a/docs/glossary.rst
+++ b/docs/glossary.rst
@@ -86,6 +86,9 @@
       A collaborative engineering organization consolidating
       and optimizing open source software and tools for the Arm architecture.
 
+   LSP
+      A logical secure partition managed by SPM
+
    MMU
       Memory Management Unit