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/resources/diagrams/plantuml/rse_attestation_flow.puml b/docs/resources/diagrams/plantuml/rse_attestation_flow.puml
index aca5c01..9d7d780 100644
--- a/docs/resources/diagrams/plantuml/rse_attestation_flow.puml
+++ b/docs/resources/diagrams/plantuml/rse_attestation_flow.puml
@@ -5,7 +5,7 @@
 participant RMM
 participant BL31
 endbox
-box RSS
+box RSE
 participant DelegAttest
 participant InitAttest
 participant MeasuredBoot