[iwm] Use chipset configuration structs like iwlwifi does.

• This makes it a bit easier to factor out common parts for e.g. the 7000 chipset family.

• Add iwm7265d config, and recognize the 7265D chipset variant via the hardware revision.

Tested:

• 7260, STA mode (2ghz)

Obtained from: Dragonflybsd commit cc8d6ccf5583fd45964f3bde9b057ee4f834c0e0