Documentation/powercap/dtpm: Add documentation for dtpm

The dynamic thermal and power management is a technique to dynamically
adjust the power consumption of different devices in order to ensure a
global thermal constraint.

An userspace daemon is usually monitoring the temperature and the
power to take immediate action on the device.

The DTPM framework provides an unified API to userspace to act on the
power.

Document this framework.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation: power: Drop reference to interface.rst

It has been merged into sleep-states.rst.

Fixes: c21502efdaed ("Documentation: admin-guide: PM: Update sleep states documentation")
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

docs: power: add it to to the main documentation index

The power docs are orphaned at the documentation body.

While it could likely be moved to be inside some guide, I'm opting to just
adding it to the main index.rst, removing the :orphan: and adding the SPDX
header.

The reason is similar to what it was done for other driver-specific
subsystems: the docs there contain a mix of Kernelspace, uAPI and
admin-guide. So, better to keep them on its own directory,
while the docs there are not properly classified.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

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

Convert the PM documents to ReST, in order to allow them to
build with Sphinx.

The conversion is actually:
- add blank lines and indentation 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>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>