KVM: selftests: Convert hypercalls test away from vm_create_default()

Use a combination of vm_create(), vm_create_with_vcpus(), and
    vm_vcpu_add() to convert vgic_init from vm_create_default_with_vcpus(),
    and away from referncing vCPUs by ID.

Thus continues the march toward total annihilation of "default" helpers.

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