nx: Don't abort on missing NX when using a QEMU machine

These don't have an NX node (and probably never will) as they
don't provide any coprocessor. However, the DARN instruction
works so this abort is unnecessary.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Stewart Smith <stewart@linux.ibm.com>

hw/nx.c

@@ -45,7 +45,8 @@ static void p9_darn_init(void)
 	dt_for_each_compatible(dt_root, nx, "ibm,power9-nx")
 		break;
 	if (!nx) {
-		assert(nx);
+		if (!dt_node_is_compatible(dt_root, "qemu,powernv"))
+			assert(nx);
 		return;
 	}