broadcom: remove old code from deprecated devices

Our current driver is focused in V3D 4.2 and 7.1, but it seems we left some code for older versions in QPU. This MR removes that code.

On top of that, and in order to keep using the convention of naming the versioned functions as v3d{42,71}_foo() this renames some functions in the QPU, as well as the lowering for image load/store.