sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

linuxkpi: Add __var_waitqueue

This returns the wait queue based on the object but in LinuxKPI
we only have one waitqueue for this.

Reviewed by: hselasky, bz
MFC after: 2 weeks
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D34250

LinuxKPI: Constantly use _LINUXKPI_ prefix in include guards

MFC after: 1 week
Reviewed by: bz, emaste, hselasky, manu
Differential Revision: https://reviews.freebsd.org/D33562

linuxkpi: Implement the wait_event_interruptible macro

This is needed by the drm-kmod 5.5 update and is similar in logic to the
existing wait_event_killable macro.

Reviewed by: hselasky, manu
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D29987

linuxkpi: Add a few wait_bit functions

The linux function does a lot more than that as multiple waitqueue could be fetch
from a static table based on the hash of the argument but since in DRM it's only used
in one place just add a single variable.
We will probably need to change that in the futur but it's ok with DRM even with current
linux.

Reviewed by: hselasky
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D26054