KVM: Add kvm_arch_vcpu_precreate() to handle pre-allocation issues

Add a pre-allocation arch hook to handle checks that are currently done
by arch specific code prior to allocating the vCPU object.  This paves
the way for moving the allocation to common KVM code.

Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/powerpc/kvm/powerpc.c

@@ -720,6 +720,11 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
 	kvmppc_core_flush_memslot(kvm, slot);
 }
 
+int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id)
+{
+	return 0;
+}
+
 struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
 {
 	struct kvm_vcpu *vcpu;