MFC r326276:

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.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Fix gcc warnings about possibly uninitialized variables in gpioctl.c.

Noticed by: bz

Make it possible for operations to refer to GPIO pins by name

- Try to guess what is provided as a pin spec for -t or for get/set
operation: number or name. Fails in case of ambiguity.
- Add -p and -N switches to force pin specification interpretation:
-p forces spec to be pin number, -N forces it to be name

Submitted by: Emmanuel Vadot <manu@bidouilliste.com>
Differential Revision: https://reviews.freebsd.org/D5201

Add a new ioctl to allow the setting of GPIO pin names.

When a gpiobus child is added, use its name to identify the mapped pin
names.

Make the respective changes to libgpio.

Add a new '-n' flag to gpioctl(8) to set the pin name.

Differential Revision: https://reviews.freebsd.org/D2002
Reviewed by: rpaulo
Requested by: many

Free the buffer returned by gpio_pin_list() after the use.

Reported by: Coverity Scan
CID: 1257468

gpioctl: don't print the command line arguments.

PR: 195330
Submitted by: Scott Ellis jumpnowtek at gmail.com
MFC after: 3 days

Rewrite parts of gpioctl(8) to use the gpio(3) library.

Assume that the -f argument is /dev/gpioc0 if it is not passed.

hrs@ provided this verison of the patch and showed me where all the needed
changes were to be made outside of gpioctl.c

Approved by: re (hrs)
MFC after: 2 weeks

More -Wmissing-variable-declarations fixes.

In addition to adding `static' where possible:

- bin/date: Move `retval' into extern.h to make it visible to date.c.
- bin/ed: Move globally used variables into ed.h.
- sbin/camcontrol: Move `verbose' into camcontrol.h and fix shadow warnings.
- usr.bin/calendar: Remove unneeded variables.
- usr.bin/chat: Make `line' local instead of global.
- usr.bin/elfdump: Comment out unneeded function.
- usr.bin/rlogin: Use _Noreturn instead of __dead2.
- usr.bin/tset: Pull `Ospeed' into extern.h.
- usr.sbin/mfiutil: Put global variables in mfiutil.h.
- usr.sbin/pkg: Remove unused `os_corres'.
- usr.sbin/quotaon, usr.sbin/repquota: Remove unused `qfname'.

Add gpioctl(8). Utility for configuring/accessing GPIO pins