dt-bindings: PCI: rockchip-dw-pcie: Prepare for Endpoint mode support

dt-bindings: PCI: rockchip-dw-pcie: Prepare for Endpoint mode support

Refactor the rockchip-dw-pcie binding to move generic properties to a new
rockchip-dw-pcie-common binding that can be shared by both RC and EP mode.

No functional change intended.

Link: https://lore.kernel.org/linux-pci/20240607-rockchip-pcie-ep-v1-v5-4-0a042d6b0049@kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>