KVM: selftests: Move the function doing Hyper-V hypercall to a common header

All Hyper-V specific tests issuing hypercalls need this.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20221101145426.251680-33-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>