AR9280/AR9285 support now working

I managed to find and fix the AR9280 and AR9285 support.

Things that needed repairing:

• Updating the AR9280 initvals to the Linux ath9k ones resolved the radio initialisation issues, making everything magically stable!
• The v4k EEPROM code (for the AR9285/AR2427) needed some surgery to reflect what was really going on. In particular, the 8 bit radio bias values in the AR9280 (v14) EEPROM are actually lots of 4 bit values; so the bias values being written to the radio were woefully incorrect. This restored AR9285 stability and made the AR2427 function.
• The AR9280 RF registers need an extra delay before being written to. I guess since the earlier radios are externally connected via single-bit IO (and thus shift registers are involved), the later radios are too. Without this delay, the AR9220 panics on my MIPS board and I would get occasional unexplained resets when I configured an AR9280 on my eeepc. This fix has resolved both those issues.

I have one more fix to integrate for the AR9220 init path so the Ubiquiti SR71-12 and SR71-15 work; then the AR9220 is supported.

The AR2427 baseband seems to hang after a few hours of use, requiring a complete cold (power off) restart. There's some more initialisation code I need to port from ath9k and there's a lot of AR9280/AR9285 calibration code which I need to port over. I hope porting these two over will fix the stability issues that I was seeing. There's also some noise floor calibration fixes from ath9k which I need to integrate into the FreeBSD-HEAD tree.

So, there's been quite a bit of progress! I've had reports from users that the AR9280, AR9285 and AR9220 support is now very stable; much more stable than before.