iwmbtfw(8): Add support for Intel 7260/7265 bluetooth adapter firmwares

To use it comms/iwmbt-firmware port should be updated to 20210315 version.

Submitted by: Philippe Michaud-Boudreault <pitwuu@gmail.com>
Tested by: Helge Oldach <freebsd@oldach.net>
Reviewed by: wulf
PR: 228787
MFC after: 2 weeks