iommu/ipmmu-vmsa: Don't register as BUS IOMMU if machine doesn't have IPMMU-VMSA

This fixes kernel crashing on NVIDIA Tegra if kernel is compiled in
a multiplatform configuration and IPMMU-VMSA driver is enabled.

Cc: <stable@vger.kernel.org> # v3.20+
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/ipmmu-vmsa.c

@@ -1108,12 +1108,19 @@ static struct platform_driver ipmmu_driver = {
 
 static int __init ipmmu_init(void)
 {
+	struct device_node *np;
 	static bool setup_done;
 	int ret;
 
 	if (setup_done)
 		return 0;
 
+	np = of_find_matching_node(NULL, ipmmu_of_ids);
+	if (!np)
+		return 0;
+
+	of_node_put(np);
+
 	ret = platform_driver_register(&ipmmu_driver);
 	if (ret < 0)
 		return ret;