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/

arm64: simplify expression

!a != !b -> a != b; this part was lifted from NetBSD, and I clearly did
not reconsider that these are bools (I'm guessing they were ints in an
earlier iteration of the NetBSD implementation).

while we're here, it should be easy to see that we've covered all of the
cases but let's add in an __assert_unreachable() to make it easier on
the eyes.

Reported by: jrtc27

arm64: emulate swp/swpb instructions

Add another undefined instruction handler for compat32 and watch out for
SWP/SWPB instructions.

SWP/SWPB were deprecated in ARMv6 and declared obsolete in ARMv7, but
this implementation is motivated by some proprietary software that still
uses SWP/SWPB. Because it's deprecated, emulation is pushed back behind
a sysctl that defaults to OFF in GENERIC so that it doesn't potentially
adversely affect package builds; it's unknown whether software may test
for a functional swp/swpb instruction with the desire of using it later,
so we err on the side of caution to ensure we don't end up with swp/swpb
use in freebsd/arm packages (which are built on aarch64).

The EMUL_SWP config option may be used to enable emulation by default in
environments where emulation is desired and won't really be turned off.

Reviewed by: andrew, mmel (both earlier version)
Sponsored by: Stormshield
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D39667

Fix the signal code on 32-bit breakpoints on arm64

When debugging 32-bit programs a debugger may insert a instruction that
will raise the undefined instruction trap. The kernel handles these
by raising a SIGTRAP, however the code was incorrect.

Fix this by using the expected TRAP_BRKPT signal code.

Sponsored by: The FreeBSD Foundation

Impleent COMPAT_FREEBSD32 for arm64.
This is based on early work by andrew@.

Move the undefined instruction handler to identcpu.c so we have access
to the registers from boot.

Approved by: re (kib)
Sponsored by: ABT Systems Ltd
Differential Revision: https://reviews.freebsd.org/D17301

Support reading from the arm64 ID registers from userspace.

Trap reads to the arm64 ID registers and write a safe value into them. This
will allow us to put more useful values in these later and have userland
check them to find what features the hardware supports.

These are currently safe defaults, but will later be populated with better
values from the hardware.

Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D16533

Add support for handling undefined instructions in userspace and the
kernel. We can register callbacks to perform the required operation on the
saved registers before returning.

This is initially used to work around a bug in old versions of QEMU that
trigger such an exception when reading from an ID register when it should
load z zero value.

I expect this could be used with other exception types, e.g. to emulate
special register access from userland.

Sponsored by: DARPA, AFRL