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>

drivers/regulator/core.c

@@ -2304,7 +2304,7 @@ static int regulator_ena_gpio_ctrl(struct regulator_dev *rdev, bool enable)
  *
  * Delay for the requested amount of time as per the guidelines in:
  *
- *     Documentation/timers/timers-howto.txt
+ *     Documentation/timers/timers-howto.rst
  *
  * The assumption here is that regulators will never be enabled in
  * atomic context and therefore sleeping functions can be used.