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/CryptoProviderClassDiagram.puml b/docs/services/uml/CryptoProviderClassDiagram.puml
new file mode 100644
index 0000000..d0176b5
--- /dev/null
+++ b/docs/services/uml/CryptoProviderClassDiagram.puml
@@ -0,0 +1,49 @@
+'-------------------------------------------------------------------------------
+' Copyright (c) 2020-2022, Arm Limited and Contributors. All rights reserved.
+'
+' SPDX-License-Identifier: BSD-3-Clause
+'
+'-------------------------------------------------------------------------------
+
+@startuml
+allow_mixing
+left to right direction
+
+
+package CryptoProvider
+{
+	class handler
+	class generate_key_handler
+	class import_key_handler
+	class sign_hash_handler
+	generate_key_handler --|> handler
+	import_key_handler --|> handler
+	sign_hash_handler --|> handler
+}
+package CryptoSerializer
+{
+	class crypto_serializer
+	class protobuf_crypto_serializer
+	class packed_c_crypto_serializer
+	protobuf_crypto_serializer --|> crypto_serializer
+	packed_c_crypto_serializer --|> crypto_serializer
+}
+package MbedCrypto
+{
+	class libmbedcrypto
+}
+package SecureStorage
+{
+	class its_client
+}
+package EntropySource
+{
+	class hw_entropy_source
+}
+
+CryptoProvider ..> CryptoSerializer
+CryptoProvider ..> MbedCrypto
+MbedCrypto ..> SecureStorage
+MbedCrypto ..> EntropySource
+
+@enduml