pan/midgard: Fix disassembly of vertex texturing on early GPUs
On T720, some registers get switched around. Let's handle this correctly. While we're at it, let's fix some issues with half-registers which were identified when trying to debug this.
With this series, shaders from e.g. dEQP-GLES2.functional.shaders.texture_functions.vertex.texture.*
should be legible.