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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

usr.sbin/pwm/pwm add support for flags

The pwm utility cant set the only flag defined (PWM_POLARITY_INVERTED) so this
patch add the option -I (capital letter i) to send it to the drivers.

None of existing PWM driver have implemented support for flags.
But soon:ish I will put up an review of a pwm driver using TI OMAP DMTimer.

Differential Revision: https://reviews.freebsd.org/D29137
MFC after: 2 weeks

pwm(8): fix potential duty overflow, use unsigneds for period and duty

For a long period value and the duty specified as a percentage,
there could be an overflow.
Using unsigned integers aligns the code with struct pwm_state and allows
to safely use periods up to 4 seconds where supported by drivers.

MFC after: 2 weeks

pwm(8): do not exit with failure after successfully reading configuration

MFC after: 1 week

Remove "all rights reserved" from copyright for the file I own.
Some of the files have both me and Jared McNeill and he gave me
permission to remove it from his files too.

Rearrange the argument checking and processing so that enable and disable
can be combined with configuring the period and duty cycle (the same ioctl
sets all 3 values at once, so there's no reason to require the user to run
the program twice to get all 3 things set).

Remove everything related to channels from the pwmc public interface, now
that there is a pwmc(4) instance per channel and the channel number is
maintained as a driver ivar rather than being passed in from userland.

Follow changes in the pwmc(4) driver in relation to device filenames.

The driver now names its cdev nodes pwmcX.Y where X is unit number and
Y is the channel within that unit. Change the default device name from
pwmc0 to pwmc0.0. The driver now puts cdev files and label aliases in
the /dev/pwm directory, so allow the user to provide unqualified names
with -f and automatically prepend the /dev/pwm part for them.

Update the examples in the manpage to show the new device name format
and location within /dev/pwm.

Make pwm channel numbers unsigned.

Move/rename the sys/pwm.h header file to dev/pwm/pwmc.h. The file contains
ioctl definitions and related datatypes that allow userland control of pwm
hardware via the pwmc device. The new name and location better reflects its
assocation with a single device driver.

pwm(8): Add percentage value support for duty cycle

pwm: Convert period and duty to unsigned int

We don't need a 64 bits value to store nanoseconds

Discused with: ian, jhibbits

pwm: Fix some arches by using %ju and casting to uintmax_t

Reported by: ci.freebsd.org

Add a pwm subsystem so we can configure pwm controller from kernel and userland.

The pwm subsystem consist of API for PWM controllers, pwmbus to register them
and a pwm(8) utility to talk to them from userland.

Reviewed by: oshgobo (capsicum), bcr (manpage), 0mp (manpage)
Differential Revision: https://reviews.freebsd.org/D17938