Refactor top-level document structure

In preparation for extending documentation on PSA certified and
secure processing environments, the top-level structure has been
cleaned-up and simplified. PNGs from tf-m for docs home have
been reused for consistency.

Signed-off-by: Julian Hall <julian.hall@arm.com>
Change-Id: Id2b7d9b46dd90f419d00c417a06003e32862ead0
diff --git a/docs/services/uml/AttestSelfGeneratedIAKflow.puml b/docs/services/uml/AttestSelfGeneratedIAKflow.puml
new file mode 100644
index 0000000..d35e8a6
--- /dev/null
+++ b/docs/services/uml/AttestSelfGeneratedIAKflow.puml
@@ -0,0 +1,22 @@
+'-------------------------------------------------------------------------------
+' Copyright (c) 2021-2022, Arm Limited and Contributors. All rights reserved.
+'
+' SPDX-License-Identifier: BSD-3-Clause
+'
+'-------------------------------------------------------------------------------
+
+@startuml
+participant "factory app"
+participant "attestation service"
+participant "keystore"
+
+hnote over "keystore": empty
+"factory app" -> "attestation service" : export_iak_public_key
+"attestation service" -> "keystore" : check_exists
+"attestation service" <-- "keystore" : false
+"attestation service" -> "attestation service" : generate_key
+"attestation service" -> "keystore" : store_key
+hnote over "keystore": provisioned
+"factory app" <-- "attestation service" : public_key
+
+@enduml