The databook clearly states that the MSI IRQ (msi_ctrl_int) is a level
triggered interrupt.
The msi_ctrl_int will be high for as long as any MSI status bit is set,
thus the IRQ type should be set to IRQ_TYPE_LEVEL_HIGH, causing the
IRQ handler to keep getting called, as long as any MSI status bit is set.
A git grep shows that ipq4019 is the only SoC using snps,dw-pcie that has
configured this IRQ incorrectly.
Not having the correct IRQ type defined will cause us to lose interrupts,
which in turn causes timeouts in the PCIe endpoint drivers.