ref-manual/qa-checks.rst: fix references

The references in this document do not work because references need to
be associated to a title. Change the bullet list into a section
separated document. This way we can cross-reference QA checks in other
parts of the documentation (it was previously failing when attempted).

The diff is a bit hard to digest, but there are no changes to content
except for:

- A fixed typo (inhert -> inherit)
- Indentation

(From yocto-docs rev: 93c30b8a430a981e8b89061c968a006a3e086353)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>