amd ryzen PR 52966

[Lars Reichardt <lars%paradoxon.info@localhost>]

I've run an updated kernel yesterday with the new (AMD) errata fixes.
(src/sys/arch/x86/x86/errata.c rev 1.24)
No patches got applied at least nothing was indicated via dmesg I
assume the firmware did apply those fixes or the zen+ has them fixed.

src/sys/arch/x86/x86/identcpu.c got patched to use FPU_SAVE_XSAVEOPT if
present and if present switch to eager fpu context switching.

With this change present I run the stream benchmark noted in
PR port-amd64/52966
without any problems on a Ryzen 2700.
Several runs while doing a release build as well as on an otherwise
idle machine. (All resulting in: "Solution validates")

para

-----
Mystische Erklärungen:
Die mystischen Erklärungen gelten für tief;
die Wahrheit ist, dass sie noch nicht einmal oberflächlich sind.

   -- Friedrich Nietzsche
   [ Die Fröhliche Wissenschaft Buch 3, 126 ]