KVM: sefltests: Use vcpu_ioctl() and __vcpu_ioctl() helpers

Use the recently introduced vCPU-specific ioctl() helpers instead of
open coding calls to ioctl() just to pretty print the ioctl name.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>