Merge branch 'mauro-warnings' into docs-next

Mauro says:

This series contain the patches from a previous series I sent:

	[PATCH v2 00/24] Documentation build fixes against next-20201013

Plus other patches I sent later, against other versions of linux-next between
20201013 and v5.10-rc1.

It fixes most of the remaining documentation build warnings.

There were some changes from v2, as I changed some patches due to the
feedback received, and added reviewed-by/acked-by to several of them.

After this series, there will be just 3 warnings at include/kunit/test.h, whose
fixes were already applied by Shuah via her tree at linux-next. Hopefully, she
will be sending it upstream anytime toon. So, I dropped the fix from my trees.

The vast majority of patches here are also on my linux-next tree, as my
original plan were to send them upstream by the end of the merge window.
I'll drop from it once they get merged.

As those patches are fixes, I guess it should be ok to get them merged for
-rc2 or -rc3.

[jc: removed DRM and JBD patches applied elsewhere]