arm64: dts: renesas: Add Renesas Draak board support

Basic support for the Renesas Draak board based on R-Car D3:
  - Memory,
  - Main crystal,
  - Serial console,
  - Watchdog.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>