PCI: dwc: Convert dw_pcie_link_up() to use dw_pcie_readl_dbi()

PCI: dwc: Convert dw_pcie_link_up() to use dw_pcie_readl_dbi()

While the rest of the generic DWC PCIe code uses the dedicated IO-mem
accessors, the dw_pcie_link_up() method for some unobvious reason directly
calls readl() to get PortLogic.DEBUG1 register content. Since the way the
DBI bus is accessed can be platform-specific, use dw_pcie_readl_dbi()
instead so dw_pcie_link_up() is slightly more generic.

Link: https://lore.kernel.org/r/20220624143428.8334-11-Sergey.Semin@baikalelectronics.ru
Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>