Add plumbing to build system and SoC level dtsi for the NRF52832 SoC. We additionally add the necessary yaml files for the UART on the NRF52 SoCs. Change-Id: I3b4a821b2993827e33d8e84bdbbc759d1521f8bd Signed-off-by: Kumar Gala <kumar.gala@linaro.org>