rockchip: add u-boot specific dts for rk3368 based boards

Device drivers like debug serial, dmc should be enabled before
relocation, so add u-boot.dtsi files to contain devices that
should be marked as dm-pre-reloc.
Signed-off-by: NAndy Yan <andy.yan@rock-chips.com>
Reviewed-by: NPhilipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: NPhilipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>

arch/arm/dts/rk3368-geekbox-u-boot.dtsi

+/*
+ * (C) Copyright 2017 Theobroma Systems Design und Consulting GmbH
+ *
+ * SPDX-License-Identifier:     GPL-2.0+	X11
+ */
+
+&pinctrl {
+	u-boot,dm-pre-reloc;
+};
+
+&service_msch {
+	u-boot,dm-pre-reloc;
+};
+
+&dmc {
+	u-boot,dm-pre-reloc;
+	status = "okay";
+};
+
+&pmugrf {
+	u-boot,dm-pre-reloc;
+};
+
+&cru {
+	u-boot,dm-pre-reloc;
+};
+
+&grf {
+	u-boot,dm-pre-reloc;
+};
+
+&uart2 {
+	u-boot,dm-pre-reloc;
+};

arch/arm/dts/rk3368-px5-evb-u-boot.dtsi

+/*
+ * (C) Copyright 2017 Theobroma Systems Design und Consulting GmbH
+ *
+ * SPDX-License-Identifier:     GPL-2.0+	X11
+ */
+
+&pinctrl {
+	u-boot,dm-pre-reloc;
+};
+
+&service_msch {
+	u-boot,dm-pre-reloc;
+};
+
+&dmc {
+	u-boot,dm-pre-reloc;
+	status = "okay";
+};
+
+&pmugrf {
+	u-boot,dm-pre-reloc;
+};
+
+&cru {
+	u-boot,dm-pre-reloc;
+};
+
+&grf {
+	u-boot,dm-pre-reloc;
+};
+
+&uart4 {
+	u-boot,dm-pre-reloc;
+};

arch/arm/dts/rk3368-sheep-u-boot.dtsi

+/*
+ * (C) Copyright 2017 Theobroma Systems Design und Consulting GmbH
+ *
+ * SPDX-License-Identifier:     GPL-2.0+	X11
+ */
+
+&pinctrl {
+	u-boot,dm-pre-reloc;
+};
+
+&service_msch {
+	u-boot,dm-pre-reloc;
+};
+
+&dmc {
+	u-boot,dm-pre-reloc;
+	status = "okay";
+};
+
+&pmugrf {
+	u-boot,dm-pre-reloc;
+};
+
+&cru {
+	u-boot,dm-pre-reloc;
+};
+
+&grf {
+	u-boot,dm-pre-reloc;
+};
+
+&uart2 {
+	u-boot,dm-pre-reloc;
+};