MFC r318001:

[iwm] include opt_iwm.h and opt_wlan.h consistently in all files.

MFC r314081:

[iwm] Switch 7265D and 3165 devices to 7265D firmware.

MFC r314076:

[iwm] Move struct iwm_cfg chipset configs to if_iwm_7000.c and _8000.c

* This is more similar to how code/definitions are distributed in
Linux's iwlwifi.

* This should make recognizing new chipset variants, and adding additional
flags from the Linux iwlwifi code easier, without blowing up if_iwm.c