Use this for the arg values at the end of your xml. Also delete the NullCPU kext. You dont need it.
<qemu:arg value='Penryn,vendor=GenuineIntel,kvm=on,+invtsc,+xgetbv1,+avx,+avx2,+aes,+xsave,+xsaveopt,+ssse3,+sse4_2,+popcnt,+bmi2,+smep,+bmi1,+fma,+movbe,vmware-cpuid-freq=on,'