sys: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

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

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

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

altera drivers: Remove unused devclass arguments to DRIVER_MODULE.

Remove unused miibus_devclass and miibus_fdt_devclass.

Convert atse(4) driver for Altera Triple-Speed Ethernet MegaCore to use
xdma(4) interface.

This allows us to switch between Altera mSGDMA or SoftDMA engines used by
atse(4) device.

This also makes atse(4) driver become 25% smaller.

Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D9618

sys/dev: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

Follow r261352 by updating all drivers which are children of simplebus
to check the status property in their probe routines.

Simplebus used to only instantiate its children whose status="okay"
but that was improper behavior, fixed in r261352. Now that it doesn't
check anymore and probes all its children; the children all have to
do the check because really only the children know how to properly
interpret their status property strings.

Right now all existing drivers only understand "okay" versus something-
that's-not-okay, so they all use the new ofw_bus_status_okay() helper.

Add a couple includes if net/if_var.h that were missed in r257176.

MFP4: 221483, 221567, 221568, 221670, 221677, 221678, 221800, 221801,
221804, 221805, 222004, 222006, 222055, 222820, 1135077, 1135118, 1136259

Add atse(4), a driver for the Altera Triple Speed Ethernet MegaCore.

The current driver support gigabit Ethernet speeds only and works with
the MegaCore only in the internal FIFO configuration in the soon to be
open sourced BERI CPU configuration.

Submitted by: bz
MFC after: 3 days
Sponsored by: DARPA/AFRL