devctl: Disable the boottime optimization of suppressing NOMATCH

The usb bus code (uhub) doens't present the same information to devctl
as it does to the NOMATCH events it generats. As such, devmatch fails to
find USB devices on boot when NOMATCH events are optimized out. Since
the savings of boot time is relatively trivial for all but the most
demanding boot environments, disable it by default until this issue is
fixed.

Fixes: 6437872c1d66
MFC After: 1 minute
Sponsored by: Netflix

New sysctl to disable NOMATCH until devmatch runs

Introduce hw.bus.devctl_nomatch_enabled and use it to suppress NOMATCH
until devmatch runs

There's a lot of NOMATCH events generated at boot. We also run devmatch
once during early boot to load unmatched devices. To avoid redundant
work, don't start generating NOMATCH events until after devmatch runs.
Set hw.bus.devctl_nomatch_enabled=1 just before we run devmatch. The
kernel will suppress NOMATCH events until this is set to true.

This saves about 170ms from the boot on aarch64 running atop Apple
M-series processors and the VMWare Fusion hypervisor.

Reviewed by: imp, cperciva
MFC after: 3 days
Sponsored by: Google Summer of Code
Pull Request: https://github.com/freebsd/freebsd-src/pull/1213

sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

devctl: allow to register a hook to receive the events

In preparation for netlink sysvent add a function that allow
registering a function to hook the events and also send it via
another kernel module (nlsysvent will be that module).

Prepare a static list of known existing events in the kernel that
will be used to prepopulate nlsysvent multicast group (one per event)

Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D37573

devd: Warn for deprecated 'kern' system type

One year ago, I deprecated 'kern' in favor of 'kernel' for the system
name for some power events. I'm about to remove it from the kernel, but
realized there's been no warning generated for users. Preserve POLA by
converting on the fly here and issuing a warning for 14.x, and an fatal
error after we branch 15. Make compiling it an error on 16 to remove
the gross hack after we branch.

Sponsored by: Netflix
Reviewed by: bapt
Differential Revision: https://reviews.freebsd.org/D37584

devd: move all devd notification logic to a separate file.

Currently, subr_bus.c shares logic for (a) maintaining all HW devices
(e.g. discovery/attach/detach logic) and (b) generic devctl notification
layer for devices/PMU/GEOM/interfaces/etc).
These two subsystems share really tiny interaction interface, composed of 3
notification functions. With that in mind, move devctl layer to a
separate file, establishing a clear notification interface between the
sub.c bus layer and the provider (devctl).

The primary driver of this change is netlink implementation (D36002).
The idea is to propagate device-level events to netlink as well, so all
netlink customers can subscribe to these changes.
The long-term goal is to deprecate devctl and to use netlink as the
kernel<> userland transport provided netlink gets enough traction.

Reviewed by: imp, markj
Differential Revision: https://reviews.freebsd.org/D36091
MFC after: 1 month