`topoext` feature missing for AMD CPUs

[JMarcosHP]

When you configure a virtual machine with cpu host-passthrough and 2 threads per core on a host system with an AMD cpu, cockpit throws the following error:

qemu-system-x86_64: warning: This family of AMD CPU doesn't support hyperthreading(2). Please configure -smp options properly or try enabling topoext feature.

SMT is enabled in the Bios of the motherboard

Editing the xml via CLI and adding this to the cpu code block, fixes the issue:

<feature policy='require' name='topoext'/>