Fix the powerpc copyout fixup from r356113

[jhibbits]

Summary

r356113 used an older patch, which predated the
freebsd_copyout_auxargs() addition. Fix this by using a private
powerpc_copyout_auxargs() instead, and keep it private to powerpc, not in MI
files.

[kib]

Thank you for fixing this.

sys/powerpc/include/elf.h

141

I would suggest to keep the symbols at the AT_ namespace, i.e. name them AT_OLD_NULL etc.

sys/powerpc/powerpc/elf_common.c

31

The file lacks $FreeBSD$ tag, which will trigger the pre-commit hook. I wrote it there because you do not need to use any includes in this file, they should be provided by consumers.

36

style issue: initialization in declaration.

[bdragon]

Tests went good.

It can boot an pre-130007 (tested with elfv2) world without crashing, and the old programs continue to work. It can also run new binaries (as expected.)

[jhibbits]

Address @kib's feedback.