irqchip/gic-v3-its: Add VPE domain infrastructure

Add the basic GICv4 VPE (vcpu in GICv4 parlance) infrastructure
(irqchip, irq domain) that is going to be populated in the following
patches.

Reviewed-by: Eric Auger <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>

drivers/irqchip/irq-gic-v3-its.c

···
 	.deactivate		= its_irq_domain_deactivate,
 };
 
+static struct irq_chip its_vpe_irq_chip = {
+	.name			= "GICv4-vpe",
+};
+
+static const struct irq_domain_ops its_vpe_domain_ops = {
+};
+
 static int its_force_quiescent(void __iomem *base)
 {
 	u32 count = 1000000;	/* 1s */
···
 	info->data = its;
 	inner_domain->host_data = info;
 
+	return 0;
+}
+
+static int its_init_vpe_domain(void)
+{
 	return 0;
 }
 
···
 		    struct irq_domain *parent_domain)
 {
 	struct device_node *of_node;
+	struct its_node *its;
+	bool has_v4 = false;
+	int err;
 
 	its_parent = parent_domain;
 	of_node = to_of_node(handle);
···
 	}
 
 	gic_rdists = rdists;
-	return its_alloc_lpi_tables();
+	err = its_alloc_lpi_tables();
+	if (err)
+		return err;
+
+	list_for_each_entry(its, &its_nodes, entry)
+		has_v4 |= its->is_v4;
+
+	if (has_v4 & rdists->has_vlpis) {
+		if (its_init_vpe_domain()) {
+			rdists->has_vlpis = false;
+			pr_err("ITS: Disabling GICv4 support\n");
+		}
+	}
+
+	return 0;
 }