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

The conversion here is really trivial: just a bunch of title
markups and very few puntual changes is enough to make it to
be parsed by Sphinx and generate a nice html.

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: Mark Brown <broonie@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

sound/soc/sof/ops.h

@@ -349,7 +349,7 @@ static inline const struct snd_sof_dsp_ops
  * @cond: Break condition (usually involving @val)
  * @sleep_us: Maximum time to sleep between reads in us (0
  *            tight-loops).  Should be less than ~20ms since usleep_range
- *            is used (see Documentation/timers/timers-howto.txt).
+ *            is used (see Documentation/timers/timers-howto.rst).
  * @timeout_us: Timeout in us, 0 means never timeout
  *
  * Returns 0 on success and -ETIMEDOUT upon a timeout. In either