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

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

Add the default hints to make the GPIO pins, rf led and reset switch work
out of the box on RouterStation.

PR: 177832
Submitted by: Petko Bordjukov (bordjukov@gmail.com)
Approved by: adrian (mentor)

Add some missing arge MDIO hints.

Submitted by: Luiz Otavio O Souza <loos.br@gmail.com>

Modify the routerstation config to use ukswitch for now.

Until an ADM6996 driver shows up, this allows for the two switch
ports to be used.

Submitted by: Luiz Otavio O Souza <loos.br@gmail.com>
Reviewed by: ray

Break out the AR71XX config file into _BASE and board specific
bits.

The ROUERSTATION and RSPRO variants contain:

* the board specific bits (eg the RTC for RSPRO, later on it'll
include the GPIO/LED definitions);
* the boot specific bits (eg, on-board flash, usb flash, etc).

For now the AR71XX_BASE file contains the common board config,
drivers and net80211/ath wireless drivers.

I'll follow this up with config files for the other boards I
have (eg the Ubiquiti LSSR71, as well as some Mikrotik boards
that use the AR71XX and atheros reference boards) which will
be quite easy to do now.