Docs: Restructure in the Platfoms section

- Move platforms' documentaions from /ext/target/ to the /platform folder
- Name arm platforms in TOC explicitly.
- Merge CS-1000 platform README with Openamp doc
- Rebase and include RSS platform

Signed-off-by: Anton Komlev <anton.komlev@arm.com>
Change-Id: If8bc343e92910e2ce94f1fe1d6c8c81802d63165
diff --git a/docs/contributing/doc_guidelines.rst b/docs/contributing/doc_guidelines.rst
index dcc9732..8c7b3b6 100644
--- a/docs/contributing/doc_guidelines.rst
+++ b/docs/contributing/doc_guidelines.rst
@@ -62,8 +62,8 @@
 The Documentation Build system provides an interface with the platform directory
 allowing maintainers to bundle platform specific documentation. **This behaviour
 needs to be explicitly enabled for each platform's space** by
-modifying the `platform/ext/index.rst` (responsible for generating the
-:doc:`Platform Index File </platform/ext/index>`) and adding a table of
+modifying the `platform/index.rst` (responsible for generating the
+:doc:`Platform Index File </platform/index>`) and adding a table of
 contents entry for the corresponding platform space.
 
 The format and structure of this entry is not strictly defined, and allows
@@ -77,7 +77,7 @@
         :caption: PLATFORM_X_CAPTION
         :glob:
 
-        target/PLATFORM_X/**
+        PLATFORM_X/**
 
 ****************
 Common Use Cases