arm: dts: actions: s700: add u-boot specific dtsi file

Devices like uart and clk are needed to be enabled before relocation.
this patch adds u-boot.dtsi file that mark these device as dm-pre-reloc.
Reviewed-by: NManivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: NAndre Przywara <andre.przywara@arm.com>
Signed-off-by: NAmit Singh Tomar <amittomer25@gmail.com>

arch/arm/dts/s700-u-boot.dtsi

+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2020 Amit Singh Tomar <amittomer25@gmail.com>
+ */
+
+/{
+	soc {
+		u-boot,dm-pre-reloc;
+	};
+};
+
+&uart3 {
+	u-boot,dm-pre-reloc;
+};
+
+&cmu {
+	u-boot,dm-pre-reloc;
+};