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

Remove /^\s*\*+\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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

Implement suword16() for the 32/64-bit PowerPC architecture.

This fixes compilation of usb(4) after 0ec590d24e415dd36e38648630a0b963412ad87e .

MFC after: 1 week
Sponsored by: NVIDIA Networking

powerpc: Fix copyin/copyout race condition

It's possible for a context switch, and CPU migration, to occur between
fetching the PCPU context and extracting the pc_curpcb. This can cause
the fault handler to be installed for the wrong thread, leading to a
panic in copyin()/copyout(). Since curthread is already in %r13, just
use that directly, as GPRs are migrated, so there is no migration race
risk.

Add CFI start/end proc directives to arm64, i386, and ppc

Follow-up to r353959 and r368070: do the same for other architectures.

arm32 already seems to use its own .fnstart/.fnend directives, which
appear to be ARM-specific variants of the same thing. Likewise, MIPS
uses .frame directives.

Reviewed by: arichardson
Differential Revision: https://reviews.freebsd.org/D27387

powerpc: Use IFUNCs for copyin/copyout/etc

Summary:
Radix on AIM, and all of Book-E (currently), can do direct addressing of
user space, instead of needing to map user addresses into kernel space.
Take advantage of this to optimize the copy(9) functions for this
behavior, and avoid effectively NOP translations.

Test Plan: Tested on powerpcspe, powerpc64/booke, powerpc64/AIM

Reviewed by: bdragon
Differential Revision: https://reviews.freebsd.org/D25129