Nix trailing whitespace in files of membars, atomics, and lock stubs.

Will be touching many of these files soon for functional changes.

No functional change intended.

Implement workaround for IBM405 Errata 77 (aka CPU_210), where
interrupted stwcx. may errantly write data to memory:

https://elinux.org/images/1/1d/Ppc405gp-errata.pdf

This is because stwcx. is split into two pieces in the pipeline.

We need to
(1) insert dcbt before every stwcx. instruction, as well as
(2) insert sync before every rfi/rfci instruction.

It is unclear which processors are affected, but according to Linux,
all 405-based cores up until 405GPR and 405EP are affected:

https://github.com/torvalds/linux/blob/master/arch/powerpc/platforms/40x/Kconfig#L140

For kernel, this workaround can be restricted to affected processors.
However, for kernel modules and userland, we have to enable it for all
32bit powerpc archs in order to share common binaries as before.

Proposed on port-powerpc:

http://mail-index.netbsd.org/port-powerpc/2020/02/21/msg003583.html

branches: 1.7.26; 1.7.28;
Reduce duplication.
Use beqlr to quicken returns

branches: 1.6.6; 1.6.12;
Use END(foo) everywhere.
Make __cerror hidden.
Use non-PLT calls to __cerror.
Use assym.h when appropriate.
Use addi to adjust stack instead of loading it.
Add __RCSIDs
Force -D_NOREGNAMES for all .S files.
[this is all in preperation for secure plt support]

enable profiling of assembly functions.

branches: 1.4.2;
Remove clause 3 and 4 from TNF licenses

branches: 1.3.4;
Use %rN as all new code is supposed to.

branches: 1.2.4;
Atomic ops for powerpc. Please review.

branches: 1.1.2;
file atomic_swap.S was initially added on branch thorpej-atomic.