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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

agp: Remove unused devclass arguments to DRIVER_MODULE.

agp: clean up empty lines in .c and .h files

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.

In agp(4) avoid the need to flush all cpu caches with wbinvd between
updating the GTT and flushing the AGP TLB by storing the GTT in
write-combining memory.

On x86 flushing the AGP TLB is done by an I/O operation or a store to a
MMIO register in uncacheable memory. Both cases imply that WC buffers are
flushed so no memory barriers are needed.

On powerpc there is no WC memory type. It maps to uncacheable memory and
two stores to uncacheable memory, such as to the GTT and then to an MMIO
register, are strongly ordered, so no memory barriers are needed either.

MFC after: 1 month

Remove unneeded header from agp: opt_bus.h

Tested with "make universe"

Approved by: cperciva
MFC after: 1 week

This isn't functionally identical. In some cases a hint to disable
unit 0 would in fact disable all units.

This reverts r241856

Approved by: cperciva (implicit)

Now that device disabling is generic, remove extraneous code from the
device drivers that used to provide this feature.

Reviewed by: des
Approved by: cperciva
MFC after: 1 week

Add a driver for the Apple Uninorth AGP host bridge found in all PowerPC
Macintoshes with an AGP bus.