Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

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

[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

- Provide necessary includes.
- Remove unnecessary includes.

Sponsored by: Netflix
Sponsored by: Nginx, Inc.

Fix the ukswitch code to work with the new vlan changes:

* Fix API changes;
* remove unused code;
* Allow some switches to be used that don't expose a set of PHY
registers for the CPU facing port (eg the ADM6996 for the Ubiquiti
Routerstation.)

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

Implement a very basic multi-PHY aware switch device.

This is intended to be used as a stop-gap for switch devices
which expose multiple ethernet PHYs but we don't have a driver
for - here, etherswitchcfg and the general switch configuration
API can be used to interface to said PHYs.

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