Add the ath0 EEPROM hints required to detect the on-chip wifi.

This allows the on-chip wifi to work; however it's not yet fully
tested.

ath0: Vendor=0x168c, Device=0x0031
ath0: Vendor=0x168c, Device=0x0031
ath0: <Atheros AR934x> at mem 0x18100000-0x1811ffff irq 0 on nexus0
...
ath0: [HT] enabling HT modes
ath0: [HT] enabling short-GI in 20MHz mode
ath0: [HT] 1 stream STBC receive enabled
ath0: [HT] 1 stream STBC transmit enabled
ath0: [HT] 2 RX streams; 2 TX streams

Tested:

* DB120 development board