Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Introduce configuration files for AP94 and AP96.

This uses the new firmware(9) method for squirreling away the EEPROM
contents from SPI flash so ath(4) can get to them later.

It won't work out of the box just yet - you have to add this to
if_ath_pci.c:

#define ATH_EEPROM_FIRMWARE

.. until I've added it as a configuration option and updated things.