dpaa2: Attach memac_mdio earlier when loading dpaa2 as a module.

It is still needed when dpaa2 compiled as a kernel module according to
my tests (not sure whether it breaks NFS root or not though).

sys/dev/dpaa2/dpaa2_mc_acpi.c

@@ -415,5 +415,7 @@ static device_method_t dpaa2_mc_acpi_methods[] = {
 DEFINE_CLASS_1(dpaa2_mc, dpaa2_mc_acpi_driver, dpaa2_mc_acpi_methods,
     sizeof(struct dpaa2_mc_softc), dpaa2_mc_driver);
 
-DRIVER_MODULE(dpaa2_mc, acpi, dpaa2_mc_acpi_driver, NULL, NULL);
+/* Make sure miibus gets procesed first. */
+DRIVER_MODULE_ORDERED(dpaa2_mc, acpi, dpaa2_mc_acpi_driver, NULL, NULL,
+    SI_ORDER_ANY);
 MODULE_DEPEND(dpaa2_mc, memac_mdio, 1, 1, 1);