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/

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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

kcov: Integrate with KMSAN

- kern_kcov.c needs to be compiled with -fsanitize=kernel-memory when
KMSAN is configured since it calls into various other subsystems.
- Disable address and memory sanitizers in kcov(4)'s coverage sanitizer
callbacks, as they do not provide useful checking. Moreover, with
KMSAN we may otherwise get false positives since the caller (coverage
sanitizer runtime) is not instrumented.
- Disable KASAN and KMSAN interceptors in subr_coverage.c, as they do
not provide any benefit but do introduce overhead when fuzzing.

Sponsored by: The FreeBSD Foundation

Generalize bus_space(9) and atomic(9) sanitizer interceptors

Make it easy to define interceptors for new sanitizer runtimes, rather
than assuming KCSAN. Lay a bit of groundwork for KASAN and KMSAN.

When a sanitizer is compiled in, atomic(9) and bus_space(9) definitions
in atomic_san.h are used by default instead of the inline
implementations in the platform's atomic.h. These definitions are
implemented in the sanitizer runtime, which includes
machine/{atomic,bus}.h with SAN_RUNTIME defined to pull in the actual
implementations.

No functional change intended.

MFC after: 1 month
Sponsored by: The FreeBSD Foundation

Mark COVERAGE and KCOV as part of KCSAN

While not strictly true this stops them from trying to use the KCSAN atomic
hooks and allows these to be compiled into the same kernel.

Sponsored by: Innovate UK

kcov: remove no longer needed atomic_load_ptr casts

Extract the coverage sanitizer KPI to a new file.

This will allow multiple consumers of the coverage data to be compiled
into the kernel together. The only requirement is only one can be
registered at a given point in time, however it is expected they will
only register when the coverage data is needed.

A new kernel conflig option COVERAGE is added. This will allow kcov to
become a module that can be loaded as needed, or compiled into the
kernel.

While here clean up the #include style a little.

Reviewed by: kib
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D18955