docs: openrisc: convert to ReST and add to documentation body

Manually convert the two openRisc documents to ReST, adding them
to the Linux documentation body.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Stafford Horne <shorne@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/openrisc/index.rst

@@ -0,0 +1,18 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================
+OpenRISC Architecture
+=====================
+
+.. toctree::
+   :maxdepth: 2
+
+   openrisc_port
+   todo
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`