Inline From/ToRGB(A) to avoid losing SSE.

Otherwise it has to store it, which I'd like to avoid.
Improve SSE usage in software transform.

It's actually already pretty decent (unlike the softgpu), but there were a
few places it could use a bit of help.  Speeds up things with hardware
transform off, or areas that need to use software transform.
Merge pull request #5677 from unknownbrackets/perf

Minor perf improvements to software transform