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>
diff --git a/include/linux/pci.h b/include/linux/pci.h
index b74b2a4..3d9a167 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -807,7 +807,7 @@ struct module;
  * @suspend_late: Put device into low power state.
  * @resume_early: Wake device from low power state.
  * @resume:	Wake device from low power state.
- *		(Please see Documentation/power/pci.txt for descriptions
+ *		(Please see Documentation/power/pci.rst for descriptions
  *		of PCI Power Management and the related functions.)
  * @shutdown:	Hook into reboot_notifier_list (kernel/sys.c).
  *		Intended to stop any idling DMA operations.