arm64: dts: cix: Enable PCIe on the Orion O6 board

arm64: dts: cix: Enable PCIe on the Orion O6 board

Add PCIe RC support on Orion O6 board.

The Orion O6 board includes multiple PCIe root complexes. The current
device tree configuration enables detection and basic operation of PCIe
endpoints on this platform.

GPIO and pinctrl subsystems for this platform are not yet ready for
upstream inclusion. Consequently, attributes such as reset-gpios and
pinctrl configurations are temporarily omitted from the PCIe node
definitions.

Endpoint detection and functionality are confirmed to be operational with
this basic configuration. The missing GPIO and pinctrl support will be
added incrementally in future patches as the dependent subsystems become
available upstream.

Acked-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Hans Zhang <hans.zhang@cixtech.com>
Link: https://lore.kernel.org/r/20251108140305.1120117-11-hans.zhang@cixtech.com
Signed-off-by: Peter Chen <peter.chen@cixtech.com>