selftests: kvm: Move kvm_get_supported_hv_cpuid() to common code

kvm_get_supported_hv_cpuid() may come handy in all Hyper-V related tests.
Split it off hyperv_cpuid test, create system-wide and vcpu versions.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210126134816.1880136-2-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>