arm64: dts: renesas: Add Si-Linux CAT874 board support

Basic support for the Si-Linux board based on RZ/G2E:
  - Memory,
  - Main crystal,
  - Serial console

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>