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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

sys/arm: 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.

Enhance the interrupt capabilities of ti_pruss driver.

The existing ti_pruss driver for the PRUSS Hardware provided by the AM335x
ARM CPU has basic interrupt capabilities. This updated driver provides some
more options:

- Sysctl based configuration for the interrupts (for some examples, see the
test plan in the phabricator review cited below).

- A device file (/dev/pruss0.irqN) for each enabled interrupt. This file
can be read and the device blocks if no irq has happened or returns an
uint64_t timestamp based on nanouptime().

- Each interrupt device file provides kqueue-based event notification,
blocking read(), or select().

Submitted by: Manuel Stuhn <freebsdnewbie@freenet.de>
Differential Revision: https://reviews.freebsd.org/D11959

ti_pruss: pass the correct IRQ to userland.

Also, fix several problems with the kqueue notification.

Submitted by: Manuel Stühn freebsdnewbie at freenet.de

Add a driver for the TI Programmable Realtime Unit Subsystem.

This is only a userland accessibility driver. It mmaps the hardware region to
userland and posts interrupt notifications via kqueue.