Using driver from Linux git HEAD would also have been the first thing I'd have tried. Sad that it doesn't solve it, so the driver is buggy or something with PCIe MMIO ranges is borked.
From first glance it looks like the driver is accessing an address in the PCIe MMIO range in 32-bit alignment (ffffffc084a1d004) but likely the SoC only supports 64-bit aligned (so only addresses ending on 0 or 8 will work) access there, hence the [ 294.051349] FSC = 0x21: alignment fault.
I've ordered the hardware and will have it in a week or two,