iwlwifi: import firmware for Intel iwlwifi/mvm supported chipsets.

Import the most recent versions of the firmware images for iwlwifi
chipsets supported by the "mvm" sub-driver.
This is based on linux-firmware at f5d519563ac9d2d1f382a817aae5ec5473811ac8.
The license of the firmware matches the previous iwnfw(4) and
iwmfw(4) firmware files and you can find a copy in
sys/contrib/dev/iwlwififw/LICENCE.iwlwifi_firmware .

Add build infrastructure to create the .ko files but do not yet hook
it up to the build until all parts are in the tree.
There is an open issue concerning kldxref that we need to resolve
(D32383).

Sponsored by: The FreeBSD Foundation

(cherry picked from commit f4c129f5fb1669b284d76a838b1e509f97c2d299)