conf: More hyperv related members into a single struct

conf: More hyperv related members into a single struct

So far, we have an array of integers (hyperv_features), an uint
(hyperv_spinlocks), a string (hyperv_vendor_id) and some tristate
switches scattered across virDomainDef. Soon, new knobs will be
introduced and keeping the current state would only worsen
readability.

Introduce virDomainHypervFeatures struct to place hyperv related
features there.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>