[ath] begin migration of AHB support to use the PCI style board data API for calibration data.

This brings the AHB support in line with the PCI support - now other "things"
can wrap up the calibration / board data into a firmware blob and have them
probe/attach after the system has finished booting.

Note that this change requires /all/ of the AHB using kernel configurations
to change - so until I drop those changes in, this breaks AHB.

Fear not, I'll do that soon.

TODO:

• the above stuff.

Tested:

• AR9331, carambola 2, loading if_ath / wlan as modules at run time