PCI: qcom-ep: Use the generic dw_pcie_ep_linkdown() API to handle Link Down event

Now that the generic dw_pcie_ep_linkdown() API is available, use it. This
also handles the reinitialization of DWC non-sticky registers in addition
to sending the notification to EPF drivers.

Link: https://lore.kernel.org/linux-pci/20240430-pci-epf-rework-v4-9-22832d0d456f@linaro.org


Tested-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Niklas Cassel <cassel@kernel.org>