FreeBSD/MIPS: AR9132 porting

I decided to avoid work a little by porting FreeBSD/MIPS to the AR9132 in the TP-LINK WN-1043nd 802.11n wireless AP I have here. There's existing OpenWRT code for it so I figured the port wouldn't be that difficult.

It turns out I was right. The AR91xx support took a couple of days to massage into a form which was good enough to commit to FreeBSD-HEAD. I also included some basic AR713x SoC support - not enough to be completely useful, but enough to get a head-start on porting.

I broke out various CPU specific operations into a set of function pointers which a CPU detection function sets up early during the MIPS init code. The main differences between the SoCs are:

* Different base frequencies for setting up RAM, peripheral bus (eg UART), etc
* Different register locations for a few things
* The AR713x has a PCIe bus; the AR71xx has a PCI bus; the AR91xx doesn't have a PCI bus
* The AR9132 has different PLL values for the gigabit ethernet MACs
* Each SoC has a different USB peripheral setup path
* Each SoC has different GPIO layouts
* There's slightly different on-board peripheral reset registers

I've tested the code on the AR71xx and AR9132 and things work fine. I now need to port the AR9100 wireless MAC support from Linux ath9k to complete things. The AR9100 looks a lot like the AR5416/AR9160 (802.11n, 3 radio chains) but it has a few annoying differences:

* It isn't on a PCI bus, so it has to be manually attached;
* A few registers differ in locations (one of which returns 0xdeadbeef if the AR5416 register location is read!)
* The EEPROM is not in the same location(s) as the AR5416 - it needs to be copied and then shoe-horned into the AR5416 eeprom access code.

Also, there's an RTL8133RB gigabit switch device on-board. There's also code in Linux/OpenWRT to support this. I'll look at porting this once the AR9100 support is done.