Memory bus width

[dhslichter]

Previous issues with DMA slowness on Kasli (m-labs/artiq#946) suggest that it would be helpful to make the memory bus wider. If Kasli-SOC is to be a higher-performance sibling of Kasli, it seems we should think about a wider memory bus (more like KC705)?

[filipswit]

Not sure what we can do with it. On KC705 bus is x64. In Kasli-SOC we connect RAM to PS only, so we have x32.