Update to 4.11.1+92-g6c33308a8d-2 with MDS documentation

Following up feedback from the release team, add a NEWS file mentioning
the MDS mitigations with some instructions, so that it will be more
visible to people using apt-listchanges.

Mention the ucode option in our default documented set of "usually used
options", so that users doing a new install will get a hint about the
existence of this option, and what it does.