irqchip/gic-v3-its: Add IORT hook for platform MSI support

Getting hold of the DevID requires us to call iort_pmsi_get_dev_id().
Since iort_pmsi_get_dev_id() may or may not be implemented, we
provide a weak function that acts as a stub.

The weak function will be removed when the ACPI counterpart is
merged.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

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

@@ -48,6 +48,11 @@ static int of_pmsi_get_dev_id(struct irq_domain *domain, struct device *dev,
 	return ret;
 }
 
+int __weak iort_pmsi_get_dev_id(struct device *dev, u32 *dev_id)
+{
+	return -1;
+}
+
 static int its_pmsi_prepare(struct irq_domain *domain, struct device *dev,
 			    int nvec, msi_alloc_info_t *info)
 {
@@ -57,7 +62,10 @@ static int its_pmsi_prepare(struct irq_domain *domain, struct device *dev,
 
 	msi_info = msi_get_domain_info(domain->parent);
 
+	if (dev->of_node)
 		ret = of_pmsi_get_dev_id(domain, dev, &dev_id);
+	else
+		ret = iort_pmsi_get_dev_id(dev, &dev_id);
 	if (ret)
 		return ret;