x86/CPU/AMD: Call the spectral chicken in the Zen2 init function

No functional change.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Link: http://lore.kernel.org/r/20231120104152.13740-6-bp@alien8.de