PCI: dwc: Ensure that dw_pcie_wait_for_link() waits 100 ms after link up

PCI: dwc: Ensure that dw_pcie_wait_for_link() waits 100 ms after link up

As per PCIe r6.0, sec 6.6.1, a Downstream Port that supports Link speeds
greater than 5.0 GT/s, software must wait a minimum of 100 ms after Link
training completes before sending a Configuration Request.

Add this delay in dw_pcie_wait_for_link(), after the link is reported as
up. The delay will only be performed in the success case where the link
came up.

DWC glue drivers that have a link up IRQ (drivers that set
use_linkup_irq = true) do not call dw_pcie_wait_for_link(), instead they
perform this delay in their threaded link up IRQ handler.

Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Wilfred Mallawa <wilfred.mallawa@wdc.com>
Link: https://patch.msgid.link/20250625102347.1205584-14-cassel@kernel.org