Switch all iwx(4) devices to -77 firmware images.

Switch all iwx(4) devices to -77 firmware images.

New firmware versions address some security issues, as outlined here:
https://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-00621.html
https://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-00699.html

Firmware has been available in fw_update for some time so systems which
track -current should already have the new -77 images.

Tested:
ax200: jmc, hrvoje, stsp
ax201: Mikhail, Sven Wolf, stsp
ax210: lraab, stsp
ax211: Mikhail, dv