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)

Bring over a configuration for the Atheros AP91 reference board.

This has an AR7240 SoC with an AR9285 wireless NIC on-board.

Since the kernel partition on the 4MiB flash is 960KiB, quite a bit
is disabled to try and squeeze the build into that. Even lzma'ed,
it's still quite large.