PCI: dwc: Add host_post_init() callback

This callback can be used by the platform drivers to do configuration
once all the devices are scanned. Like changing LNKCTL of all downstream
devices to enable ASPM etc...

Link: https://lore.kernel.org/linux-pci/20231010155914.9516-2-manivannan.sadhasivam@linaro.org


Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>