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

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

Since these include wlan/ath/ah headers and these can change
definitions based on the state of the kernel compile environment,
ensure the opt_*.h files are available.

Break out the ath PCI logic into a separate device/module.

Introduce the AHB glue for Atheros embedded systems. Right now it's
hard-coded for the AR9130 chip whose support isn't yet in this HAL;
it'll be added in a subsequent commit.

Kernel configuration files now need both 'ath' and 'ath_pci' devices; both
modules need to be loaded for the ath device to work.