[libvirt] xsave-related CPU features implementation

[Alexander Burluka]

Hello,

I would like to add support for the next CPU features which presents in
QEMU - xsaveopt, xsavec, xgetbv1, xsaves. These features were introduced
in QEMU commit 0bb0b2d2fe7f645ddaf1f0ff40ac669c9feb4aa1.
I was confused by comment in src/cpu/cpu_map.xml:
...
<!-- We support only ecx 0x0 now as it's done by a workaround -->
...
Is this comment is still actual? This feature set needs ecx 0x1.
I can see that it was a temporary solution in commit by Peter Krempa
012f9b19ef3812884e207dc431571502de4cebce. Does these features addtion
require CPU detection improvement? Or can I simply put them into 
src/cpu/cpu_map.xml?

Thank you

-- 
Regards,
Alexander Burluka