PCI: dwc: Implement .assert_perst() for dwc glue drivers

PCI: dwc: Implement .assert_perst() for dwc glue drivers

Add .assert_perst() hook for dwc glue drivers to register with
assert_perst() of pci ops, allowing for better control over the link
initialization and shutdown process.

Implement assert_perst() function op for dwc drivers.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
[bhelgaas: squash dwc host support]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20251101-tc9563-v9-3-de3429f7787a@oss.qualcomm.com
Link: https://patch.msgid.link/20251101-tc9563-v9-4-de3429f7787a@oss.qualcomm.com