brppt1: Cleanup device tree

* Remove unnecessary device tree nodes which are not needed in
  U-Boot directly.
* Move all U-Boot specific device tree properties to u-boot dtsi.

Signed-off-by: Bernhard Messerklinger <bernhard.messerklinger@br-automation.com>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>