VS/PS_NUM_REG is 6-bit on Adreno 200, and games aren't seen using the
bit 7 to indicate that no GPRs are used. It's not clear why Freedreno
configures it this way.
Some texture fetch fields were deprecated or moved during the development
of the Xenos, reflect that in the comments.
Add definitions of the registers configuring the conversion of vertex
positions to fixed-point. Although there isn't much that can be done with
it when emulating using PC GPU APIs, there are some places in Xenia that
wrongly (though sometimes deliberately, for results closer to the behavior
of the host GPU) assume that the conversion works like in Direct3D 10+,
however the Xenos supports only up to 4 subpixel bits rather than 8. The
effects of this difference are largely negligible, though.
Also add more detailed info about register references and differences from
other ATI/AMD GPUs for potential future contributors.
Document research about viz queries.
v2: Remove viz status unions and move comments to register definitions.
Add contributors to TODOs.
v3: Comment out unused variables.
Add TODO for correctly dropping draw calls with memexport.
Register comment formatting.
