PCI: rockship-ep: Implement the pci_epc_ops::stop_link() operation

PCI: rockship-ep: Implement the pci_epc_ops::stop_link() operation

Define the EPC operation ->stop() for the Rockchip endpoint driver with
the function rockchip_pcie_ep_stop(). This function disables link
training and the controller configuration, as the reverse to what
the start operation defined with rockchip_pcie_ep_start() does.

Link: https://lore.kernel.org/r/20241017015849.190271-12-dlemoal@kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>