Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

sys/dev: minor spelling fixes.

Most affect comments, very few have user-visible effects.

[mdio] migrate mdiobus out of etherswitch and into a top-level device of its own.

The mdio driver interface is generally useful for devices that require
MDIO without the full MII bus interface. This lifts the driver/interface
out of etherswitch(4), and adds a mdio(4) man page.

Submitted by: Landon Fuller <landon@landonf.org>
Differential Revision: https://reviews.freebsd.org/D4606

Introduce e6000sw etherswitch support

Add e6000sw driver supporting Marvell 88E6352, 88E6172, 88E6176 switches.
It needs to be attached to mdio interface, exporting SMI access
functionality. e6000sw supports port-based VLAN configuration, per-port
media changing, accessing PHY and switch registers.

e6000sw attaches miibuses and PHY drivers as children. Instead of typical
tick as callout, kthread-based tick is used. This combined with SX locks
allows MDIO read/write calls to sleep. It is expected, because this
hardware requires long delays in SMI read/write procedures, which can not
be handled by busy-waiting.

Reviewed by: adrian
Obtained from: Semihalf
Submitted by: Bartosz Szczepanek <bsz@semihalf.com>
Differential revision: https://reviews.freebsd.org/D3902