ARM: dts: iwg20d-q7: Enable PCIe Controller

Enable PCIe Controller & set PCIe bus clock frequency.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>