arm64: dts: mediatek: mt8188: Add PCIe nodes

Add PCIe node and the associated PHY node.
Individual board device tree should enable the nodes as needed.

Reviewed-by: Macpaul Lin <macpaul.lin@mediatek.com>
Signed-off-by: Fei Shao <fshao@chromium.org>
Link: https://lore.kernel.org/r/20241014111053.2294519-3-fshao@chromium.org


Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>