This makes it easier to move around for future optimizations, and it already gains us a few FPS by allowing the compiler to optimize a little better

Sometimes we might want host-side software to control it, or even to just turn it off.

This makes the mapping from 16-bit color to LUT entry straightforward, while still fully defining the entire range from 0x0000 through 0xFFFF. This fixes an edge case where colors greater than 0xFF00 would wrap past the end of the R/G LUTs onto the next color channel.

This reverts commit 07106959.

This reverts commit f5e7cc2e.

This actually makes us slightly slower, due to increased register pressure, but I think if I can alleviate that we'll see a speedup.

Almost fast enough.. just 1.3ms more to shave off per frame.