Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

Fix style(9) space vs tab.

Reviewed by: jhb
MFC after: 3 weeks.
Sponsored by: iXsystems Inc.
Differential Revision: https://reviews.freebsd.org/D15768

various: general 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.

No functional change intended.

Polish AHCI disk identify data and fix speed negotiation.

MFC after: 2 weeks

Import Zhixiang Yu's GSoC'13 AHCI emulation:
https://wiki.freebsd.org/SummerOfCode2013/bhyveAHCI

This provides ICH8 SATA disk and ATAPI ports, selectable
via the bhyve slot command-line parameter:

SATA
-s <slot>,ahci-hd,<image-file>

ATAPI
-s <slot>,ahci-cd,<image-file>

Slight modifications by: grehan@
Approved by: re@ (blanket)
Obtained from: FreeBSD GSoC'13