XML:
<features>
  <hyperv>
    <vapic state='on'/>
    <spinlocks state='on' retries='4096'/>
  </hyperv>
</features>

results in the following QEMU command line:
qemu -cpu <cpu_model>,hv_vapic,hv_spinlocks=0x1000

https://bugzilla.redhat.com/show_bug.cgi?id=784836