docs: change all occurrences of RSS to RSE

Changes all occurrences of "RSS" and "rss" in the documentation
to "RSE" and "rse".

Signed-off-by: Tamas Ban <tamas.ban@arm.com>
Change-Id: Ia42078f5faa1db331b1e5a35f01faeaf1afacb5f
diff --git a/docs/threat_model/supply_chain_threat_model.rst b/docs/threat_model/supply_chain_threat_model.rst
index 386a4b0..a0fed5c 100644
--- a/docs/threat_model/supply_chain_threat_model.rst
+++ b/docs/threat_model/supply_chain_threat_model.rst
@@ -115,7 +115,7 @@
 - *EDK2 UEFI*: Normal world bootloader from the EDK2 project [7]_. We use EDK2
   UEFI binaries hosted on tf.org servers for testing [8]_.
 
-Other software components used to test TF-A include U-Boot, Linux kernel, RSS,
+Other software components used to test TF-A include U-Boot, Linux kernel, RSE,
 MCP, and file systems, all sourced from the Arm Reference Platforms teams.
 
 TF-A Toolchain