PCI: dw-rockchip: Enumerate endpoints based on dll_link_up IRQ

Most boards using the pcie-dw-rockchip PCIe controller lack standard
hotplug support.

Thus, when an endpoint is attached to the SoC, users have to rescan the bus
manually to enumerate the device. This can be avoided by using the
'dll_link_up' interrupt in the combined system interrupt 'sys'.

Once the 'dll_link_up' IRQ is received, the bus underneath the host bridge
is scanned to enumerate PCIe endpoint devices.

This implements the same functionality that was implemented in the DWC
based pcie-qcom driver in 4581403f ("PCI: qcom: Enumerate endpoints
based on Link up event in 'global_irq' interrupt").

The Root Complex specific device tree binding for pcie-dw-rockchip already
has the 'sys' interrupt marked as required, so there is no need to update
the device tree binding. This also means that we can request the 'sys' IRQ
unconditionally.

Link: https://lore.kernel.org/r/20241127145041.3531400-2-cassel@kernel.org


Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
[bhelgaas: commit log, squash Pei Xiao's redundant dev_err() fix from
https://lore.kernel.org/r/327718207d3cd72847c079ff9d56eb246744c182.1736126067.git.xiaopei01@kylinos.cn,
squash Niklas's #define change from https://lore.kernel.org/r/20250103095812.2408364-2-cassel@kernel.org

]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>