Enable support for the Renesas RZN1D-DB Board:
  - RZ/N1D (R9A06G032) base SoC support,
  - Synopsys DesignWare 8250 serial port support.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>