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: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Amit Singh Tomar <amittomer25@gmail.com>