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

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

Hint miibus to attach arswitch on AP91, AP93 and RSPRO boards.

Submitted by: Luiz Otavio O Souza
Approved by: adrian (menthor)

Enable the AR8316 switch on the routerstation pro board.

The configuration is:

* RGMII, both ports
* arge0 - connected to PHY4 as a dedicated port (CPU port)
* arge1 - connected to the switch ports

I've verified this on my routerstation pro board.

Flesh out the RSPRO GPIO config, including the RF LED.

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.