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/

linuxkpi: Define `hrtimer_try_to_cancel()`

It is the same as callout_stop(9) but the return values are different.

Reviewed by: hselasky
Approved by: hselasky
Differential Revision: https://reviews.freebsd.org/D38081

compat: clean up empty lines in .c and .h files

Improve high resolution timer support in the LinuxKPI.

Submitted by: Johannes Lundberg <johalun0@gmail.com>
MFC after: 1 week
Sponsored by: Mellanox Technologies
Sponsored by: Limelight Networks

Remove "All rights reserved" from my files.

See r333391 for the rationale.

MFC after: 1 week

Update the ktime type in the LinuxKPI to be a signed 64-bit integer similarly
to Linux, to avoid compilation issues. Implement ktime_get_real_seconds().

MFC after: 1 week
Submitted by: Johannes Lundberg <johalun0@gmail.com>
Sponsored by: Mellanox Technologies
Sponsored by: Limelight Networks

Fix hrtimer_active() in case of cancellation.

While there, switch to FreeBSD internal callout active status.

Reviewed by: markj, hselasky
Sponsored by: iXsystems, Inc.
Differential Revision: https://reviews.freebsd.org/D11900

Add inline functions to convert between sbintime_t and decimal time units.
Use them in some existing code that is vulnerable to roundoff errors.

The existing constant SBT_1NS is a honeypot, luring unsuspecting folks into
writing code such as long_timeout_ns*SBT_1NS to generate the argument for a
sleep call. The actual value of 1ns in sbt units is ~4.3, leading to a
large roundoff error giving a shorter sleep than expected when multiplying
by the trucated value of 4 in SBT_1NS. (The evil honeypot aspect becomes
clear after you waste a whole day figuring out why your sleeps return early.)

Implement parts of the hrtimer API in the LinuxKPI.

Reviewed by: hselasky
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D11359