MFC r331245:
Drop KTR_CONTENTION.

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

ioat: Introduce KTR probes

Sponsored by: EMC / Isilon Storage Division

Add KTR tracing for some MI ptrace events.

Differential Revision: https://reviews.freebsd.org/D2643
Reviewed by: kib

give others fair warning that _SPARE2 isn't just cxgb, but used by large
number of other subsystems, so you probably don't want _SPARE2..

ktr needs an overhaul to really only compile in the ones you want,
we've long passed the 31 bits it provides..

Sponsored by: transip.nl

Right now LOCK_DEBUG is enabled if KTR is on.
This is to support LOCK_LOG_* functionality effectively in debugging
environments but it is overkill because really LOCK_DEBUG should be on
only if (KTR_COMPILE & KTR_LOCK) is true.
Fix this by applying the correct logic.
In this process, move the KTR classes to its own header to reduce
namespace pollution.

Sponsored by: EMC / Isilon storage division
Reviewed by: jhb