PCI: dwc: Pass DWC PCIe mode to dwc_pcie_debugfs_init()

Upcoming PTM debugfs interface relies on the DWC PCIe mode to expose the
relevant debugfs attributes to userspace. So pass the mode to
dwc_pcie_debugfs_init() API from host and ep drivers and save it in
'struct dw_pcie::mode'.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Link: https://patch.msgid.link/20250505-pcie-ptm-v4-2-02d26d51400b@linaro.org