sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

Update VMCI license based on comments from core, the FreeBSD Foundation,
and VMware legal:
- Add a dual BSD-2 Clause/GPLv2 LICENSE file in the VMCI directory
- Remove the use of "All Rights Reserved"
- Per best practice, remove copyright/license info from Makefile

Reviewed by: imp, emaste, jhb, Vishnu Dasa <vdasa@vmware.com>
Approved by: VMware legal via Mark Peek <markpeek@vmware.com>
Differential Revision: https://reviews.freebsd.org/D14979

Rectify VMCI SPDX license

Approved by: Vishnu Dasa <vdasa@vmware.com>

vmci(4): Fix GCC build and rationalize vmci_kernel_defs.h

To fix the GCC build, remove multiple redundant declarations of
vmci_send_datagram() (the copy in vmci.h as well as the extern definition in
vmci_queue_pair.c were wholly redundant).

Also to fix the GCC build, include a non-empty format string in the vmci(4)
definition of ASSERT(). It seems harmless either way, but adding the
stringified invariant is easier than masking the warning.

The other vmci_kernel_defs.h changes are cosmetic and simply match macros to
existing definitions.

Reported by: GCC 6.4.0
Sponsored by: Dell EMC Isilon

Add VMCI (Virtual Machine Communication Interface) driver

In a virtual machine, VMCI is exposed as a regular PCI device. The primary
communication mechanisms supported are a point-to-point bidirectional
transport based on a pair of memory-mapped queues, and asynchronous
notifications in the form of datagrams and doorbells. These features are
available to kernel level components such as vSockets through the VMCI
kernel API. In addition to this, the VMCI kernel API provides support for
receiving events related to the state of the VMCI communication channels,
and the virtual machine itself.

Submitted by: Vishnu Dasa <vdasa@vmware.com>
Reviewed by: bcr, imp
Obtained from: VMware
Differential Revision: https://reviews.freebsd.org/D14289