virt: detect KubeVirt instance
    
    Kubevirt is currently technically based on KVM (but not xen yet[1]).
    The systemd-detect-virt command, used to differentiate the current
    virtualization environment, works fine on x86 relying on CPUID, while
    fails to get the correct value (none instead of kvm) on aarch64.
    
    Let's fix this by adding a new 'vendor[KubeVirt] = kvm' classification
    considering the sys_vendor is always KubeVirt.
    
    [1] https://groups.google.com/g/kubevirt-dev/c/C6cUgzTOsVg
    
    Signed-off-by: Fei Li <lifei.shirley@bytedance.com>
    (cherry picked from commit c15d1ac2c4e8ce46c6d07621f7d5531cbc2160a8)