iwlwifi: update from iwlwifi-next

Import new code from iwlwifi-next at cb0a1fb7fd86b0062692b5056ca8552906509512
(matching tag: iwlwifi-next-for-kalle-2022-02-18).

Also add files not previously imported because we are not yet compiling
them to ease updating and having them when needed.

This adds MEI (Management Engine) support upstream which we cannot import
(currently GPL-only) so we have stub functions for the missing bits.

This also reduces the diff to upstream. Changes submitted to avoid
problems with const and with void * arithmetics were merged.

In the module build Makefile disable CONFIG_IWLWIFI_OPMODE_MODULAR
as we are building iwlwifi as a single module.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days