cpu: Add recently added cpu feature flags.

cpu: Add recently added cpu feature flags.

Qemu has added some new feature flags. This patch adds them to libvirt.

The new features are for the cpuid function 0x7 that takes an argument
in the ecx register. Currently only 0x0 is used as the argument so I was
lazy and I just clear the registers to 0 before calling cpuid. In future
when there maybe will be some other possible arguments, we will need to
improve the cpu detection code to take this into account.