x86jit: More fixes / tweaks to simd

This:
  * Fixes my recent optimization to apply dirty.
  * Corrects dirty in lv.s and a few other places using only MAP_NOINIT or 0 explicitly.
  * Corrects dirty in a few more regs that I thought handled it.
  * Enables dirty-checking for FPU and VFPU (would appreciate testing, things seem to work for me, and I went over both carefully.)
  * Switches VS() and VSX() to take `const u8 *` regs.

Doesn't turn on simd again, but might be safe now.  Would like to know how Tekken reacts (with `enableVFPUSIMD = true;`.)

-[Unknown]