powerpc: dts: t2080rdb: tag serial nodes with bootph-all

Make sure the serial driver is initialized before relocation by tagging
the serial nodes with "bootph-all". Add these u-boot specific properties
to an *-u-boot.dtsi file.

Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/powerpc/dts/t2080rdb-u-boot.dtsi b/arch/powerpc/dts/t2080rdb-u-boot.dtsi
new file mode 100644
index 0000000..b50b922
--- /dev/null
+++ b/arch/powerpc/dts/t2080rdb-u-boot.dtsi
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* Copyright 2023 NXP */
+
+&serial0 {
+	bootph-all;
+};
+
+&serial1 {
+	bootph-all;
+};
+
+#include "u-boot.dtsi"