arm64: dts: hisilicon: add dts files for hi3798cv200-poplar board

Add basic dts files for hi3798cv200-poplar board. Poplar is the
first development board compliant with the 96Boards Enterprise
Edition TV Platform specification. The board features the
Hi3798CV200 with an integrated quad-core 64-bit ARM Cortex A53
processor and high performance Mali T720 GPU.

Signed-off-by: Jiancheng Xue <xuejiancheng@hisilicon.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Acked-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>