docs: misc-devices/pci-endpoint-test.txt: convert to ReST

- Use titles markups;
- Adjust identation;
- use literal markup;
- Use the proper notation for footnotes.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/d4def59b3e3042208ed44558ddfd96c8753fb88c.1592203650.git.mchehab+huawei@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>