arm64: dts: renesas: r8a774c0: Add PCIe device node

This patch adds PCI express channel 0 device tree node to the
RZ/G2E (a.k.a. R8A774C0) SoC dtsi.

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