Add initial support for the AR9485 CUS198 / CUS230 variants.

These variants have a few differences from the default AR9485 NIC,
namely:

* a non-default antenna switch config;
* slightly different RX gain table setup;
* an external XLNA hooked up to a GPIO pin;
* (and not yet done) RSSI threshold differences when
  doing slow diversity.

To make this possible:

* Add the PCI device list from Linux ath9k, complete with vendor and
  sub-vendor IDs for various things to be enabled;
* .. and until FreeBSD learns about a PCI device list like this,
  write a search function inspired by the USB device enumeration code;
* add HAL_OPS_CONFIG to the HAL attach methods; the HAL can use this
  to initialise its local driver parameters upon attach;
* copy these parameters over in the AR9300 HAL;
* don't default to override the antenna switch - only do it for
  the chips that require it;
* I brought over ar9300_attenuation_apply() from ath9k which is cleaner
  and easier to read for this particular NIC.

This is a work in progress.  I'm worried that there's some post-AR9380
NIC out there which doesn't work without the antenna override set as
I currently haven't implemented bluetooth coexistence for the AR9380
and later HAL.  But I'd rather have this code in the tree and fix it
up before 11.0-RELEASE happens versus having a set of newer NICs
in laptops be effectively RX deaf.

Tested:

* AR9380 (STA)
* AR9485 CUS198 (STA)

Obtained from:	Qualcomm Atheros, Linux ath9k