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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

gpio: Remove unused devclass arguments to DRIVER_MODULE.

Move the pl061 acpi attachment earlier

As the pl061 driver can be an interrupt controller attach it earlier in the
boot so other drivers can use it.

Use a new GPIO xref to not conflict with the existing root interrupt
controller.

Sponsored by: Innovate UK

Switch the name of the pl061 driver to gpio

We need it to be named gpio for gpiobus to work.

Sponsored by: Innovate UK

Add a GPIO driver for the Arm pl061 controller

A PL061 is a simple 8 pin GPIO controller. This GPIO device is used to
signal an internal request for shutdown on some virtual machines including
Arm-based Amazon EC2 instances.

Submitted by: Ali Saidi <alisaidi_amazon.com> (previouss version)
Reviewed by: Ali Saidi, manu
Differential Revision: https://reviews.freebsd.org/D24065