PCI: dwc: Use native DWC IP core version representation

Save the DWC IP core version in the same format as the
PORT_LOGIC.PCIE_VERSION_OFF register, similar to what other drivers for DWC
IP do (dw_spi_hw_init(), dwc3_core_is_valid(), stmmac_hwif_init()).

[bhelgaas: trim commit log]
Link: https://lore.kernel.org/r/20220624143947.8991-4-Sergey.Semin@baikalelectronics.ru


Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>