x86jit: Add basic support for mapping SIMD

This implements only the VecDo3 ops using SIMD.  It seems to work from the games I've tested.

I'd like to simplify though.  I'm thinking it'd be better to change this pattern:

```c++
	VectorSize sz = GetVecSize(op);
	int n = GetNumVectorElements(sz);

	u8 sregs[4], tregs[4], dregs[4];
	GetVectorRegsPrefixS(sregs, sz, _VS);
	GetVectorRegsPrefixT(tregs, sz, _VT);
	GetVectorRegsPrefixD(dregs, sz, _VD);

	if (fpr.TryMapDirtyInInVS(dregs, sz, sregs, sz, tregs, sz)) {
		...

		ApplyPrefixD(dregs, sz);
		fpr.ReleaseSpillLocks();
		return;
	}

	// Flush SIMD.
	fpr.SimpleRegsV(sregs, sz, 0);
	fpr.SimpleRegsV(tregs, sz, 0);
	fpr.SimpleRegsV(dregs, sz, MAP_NOINIT | MAP_DIRTY);

	...

	ApplyPrefixD(dregs, sz);

	fpr.ReleaseSpillLocks();
```

To something more like:

```c++
	// Things like: VECREGS_D_LOAD, VECREGS_DSZ_HALF, VECREGS_NO_PREFIX, etc...
	VecOpRegs regs = GetVectorRegs(op, VECREGS_DST);

	if (fpr.TryMapVS(regs)) {
		...

		// Or maybe done automatically if mapped?  Just worried about DISABLE.
		regs.FinalizeD();
		return;
	}

	fpr.SimpleRegsV(regs);

	...

	regs.FinalizeD();
```

And also matrices... those are complicated...

-[Unknown]
Hm. As you are doing this several times to the same register, won't the rotation "compound"? That is, you should rotate by 1 each time through the loop instead of rotating by n?