- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

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

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

Bring over the first part of the etherswitch framework - an MDIO bus and
MDIO/MII rendezvous proxy.

* Add an 'mdio' bus, which is the "IO" side of an MII bus (but by design
can be anything which implements the underlying register access API.)
* Add 'miiproxy' and 'mdioproxy', which provides a rendezvous mechanism
for MII busses to appear hanging off arbitrary busses (ie, that aren't
necessarily a traditional looking MII bus.)

MII busses can now hang off anything that implements an mdiobus.

For the AR71xx SoC, there's one MDIO bus but two MII busses. So to
properly support two or more real PHYs, this can be done:

# arge0 MDIO bus - there's no arge1 MDIO bus for AR71xx
hint.argemdio.0.at="nexus0"
hint.argemdio.0.maddr=0x19000000
hint.argemdio.0.msize=0x1000
hint.argemdio.0.order=0

# Create two mdioproxy instances
hint.mdioproxy.0.at="mdio0"
hint.mdioproxy.1.at="mdio0"

# .. and with a follow-up patch
hint.arge.0.mdio=mdioproxy0
hint.arge.1.mdio=mdioproxy0

TODO:

* Do a sweep or two and add appropriate locking in mdio/mdioproxy/miiproxy.

Submitted by: Stefan Bethke <stb@lassitu.de>
Reviewed by: ray