scripts: compliance: add sphinx-lint linter

ReStructuredText can sometimes be tricky to get right, especially for
folks that might be more familiar with Markdown.

This adds a Sphinx/RST linter to the compliance check script to help
catch common issues that can easily go unnoticed and cause rendering
issues.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>
4 files changed