docs: locking: convert docs to ReST and rename to *.rst

Convert the locking documents to ReST and add them to the
kernel development book where it belongs.

Most of the stuff here is just to make Sphinx to properly
parse the text file, as they're already in good shape,
not requiring massive changes in order to be parsed.

The conversion is actually:
  - add blank lines and identation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Federico Vaga <federico.vaga@vaga.pv.it>
diff --git a/Documentation/kernel-hacking/locking.rst b/Documentation/kernel-hacking/locking.rst
index dc698ea..a8518ac0 100644
--- a/Documentation/kernel-hacking/locking.rst
+++ b/Documentation/kernel-hacking/locking.rst
@@ -1364,7 +1364,7 @@
 Further reading
 ===============
 
--  ``Documentation/locking/spinlocks.txt``: Linus Torvalds' spinlocking
+-  ``Documentation/locking/spinlocks.rst``: Linus Torvalds' spinlocking
    tutorial in the kernel sources.
 
 -  Unix Systems for Modern Architectures: Symmetric Multiprocessing and