RK3576 DFI Support

RK3576, like other Rockchip SoCs, has support for DFI. This allows tracking the current memory bandwidth consumption through a perf interface. According to the mainline status matrix, "upstream driver needs few changes".

I currently have some stuff inflight that targets that driver with the LPDDR5 part of #36 and the hiword series, but after that it should probably be fine to work on this.