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

- use title markups;
- mark literal blocks.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/1b1f4e5e57fd2065828cecc9d07afbd247349e94.1592203650.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>