PCI: rockchip-ep: Improve rockchip_pcie_ep_map_addr()

Add a check to verify that the outbound region to be used for mapping an
address is not already in use.

Link: https://lore.kernel.org/r/20241017015849.190271-5-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>