KVM: selftests: Avoid memory allocations when adding vCPU in get-reg-list

Open code adding and doing setup for a vCPU in get-reg-list in order to
avoid the stack allocation that comes with aarch64_vcpu_add_default().
get-reg-list doesn't need to run the vCPU, and so doesn't need the guest
to be backed with memory.  This will allow future cleanup to turn what is
current vm_create() into a barebones helper.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/aarch64/get-reg-list.c

@@ -418,7 +418,8 @@ static void run_test(struct vcpu_config *c)
 
 	vm = vm_create(DEFAULT_GUEST_PHY_PAGES);
 	prepare_vcpu_init(c, &init);
-	aarch64_vcpu_add_default(vm, 0, &init, NULL);
+	vm_vcpu_add(vm, 0);
+	aarch64_vcpu_setup(vm, 0, &init);
 	finalize_vcpu(vm, 0, c);
 
 	reg_list = vcpu_get_reg_list(vm, 0);