PCI: qcom: Enumerate endpoints based on Link up event in 'global_irq' interrupt

Historically, Qcom PCIe RC controllers lacked standard hotplug support. So
when an endpoint is attached to the SoC, users have to rescan the bus
manually to enumerate the device. But this can be avoided by using the Link
up event exposed by the Qcom specific 'global_irq' interrupt.

Qcom PCIe RC controllers are capable of generating the 'global' SPI
interrupt to the host CPUs. The device driver can use this interrupt to
identify events such as PCIe link specific events, safety events etc...

One such event is the PCIe Link up event generated when an endpoint is
detected on the bus and the Link is 'up'. This event can be used to
enumerate the PCIe endpoint devices without user intervention.

So add support for capturing the PCIe Link up event using the 'global'
interrupt in the driver. Once the Link up event is received, the bus
underneath the host bridge is scanned to enumerate PCIe endpoint devices.

All of the Qcom SoCs have only one Root Port per controller instance. So
only a single 'Link up' event is generated for the PCIe controller.

Link: https://lore.kernel.org/linux-pci/20240828-pci-qcom-hotplug-v4-11-263a385fbbcb@linaro.org


Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>