sys: Remove $FreeBSD$: one-line .c comment pattern

Remove /^/[*/]\s*\$FreeBSD\$.*\n/

LinuxKPI: move pm_message_t from kernel.h to pm.h

Move pm_message_t from kernel.h to pm.h and remove a private define
in usb.h as well as adjust the implementation in linux_usb.c.
This cleans up what I believe to be a historic shortcut and is
needed for future wireless driver updates.

Leave a note in UPDATING that drm-kmod users need to update to the
latest version before re-compiling a new kernel to avoid errors
(see PR).

Sponsored by: The FreeBSD Foundation
MFC after: 3 days
PR: 264449 (drm-kmod port update, thanks wulf)
Obtained from: bz_git_iwlwifi (Dec 2020) (partly)
Reviewed by: hselasky, imp
Differential Revision: https://reviews.freebsd.org/D35276

linuxkpi whitespace cleanup

Reviewed by: hselasky, markj
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D14807

Make all the LinuxKPI include files compile standalone.

Sponsored by: Mellanox Technologies

Finish process of moving the LinuxKPI module into the default kernel build.

- Move all files related to the LinuxKPI into sys/compat/linuxkpi and
its subfolders.
- Update sys/conf/files and some Makefiles to use new file locations.
- Added description of COMPAT_LINUXKPI to sys/conf/NOTES which in turn
adds the LinuxKPI to all LINT builds.
- The LinuxKPI can be added to the kernel by setting the
COMPAT_LINUXKPI option. The OFED kernel option no longer builds the
LinuxKPI into the kernel. This was done to keep the build rules for
the LinuxKPI in sys/conf/files simple.
- Extend the LinuxKPI module to include support for USB by moving the
Linux USB compat from usb.ko to linuxkpi.ko.
- Bump the FreeBSD_version.
- A universe kernel build has been done.

Reviewed by: np @ (cxgb and cxgbe related changes only)
Sponsored by: Mellanox Technologies