EMI: PS2 version fixes

Previously all 5551 format textures became half-transparent after conversion to 32-bit, because the color conversion in the case of 1-bit alpha was wrong. bd5d9c9 fixes the issue. This is again a change that could be sent  to ScummVM too.

This PR also fixes movement after the prologue, and some crashes. I also have fixes for the sound [in this branch](https://github.com/Akz-/residual/commits/emi-ps2-fixes), but I'll probably merge those into my sounds PR.