iwlwifi: import Intel's iwlwifi/mvm driver.

Over the past few months we published multiple snapshots for this
Linux derived driver and it has become fairly stable in terms of
minimal local changes needed for new updates.

The current version is based on iwlwifi-next update at
cbaa6aeedee5f92dafa5982eceea2a1f98ce4f7d with the addition of
a hand full of files replaced for FreeBSD.

Given the lack of full license texts on non-local files this is
imported under the draft policy for handling SPDX files (D29226). [1]

Do not yet hook this to the build until the remaining compat code
is all in. Along with the firmware import this will make publishing
the last bits and final testing a lot easier.

Sponsored by: The FreeBSD Foundation
Approved by: core (imp) [1]
MFC after: 10 days