x86jit: Implement other forms of vx2i

Gains 3.2% fps in Grand Knights History.  And I should note, that's with it spending > 50% of its time dealing with graphics, single threaded (30% overall hashing textures, in fact.)  With the other changes, up to 1020% now.

This also marks the first usage of > SSE2 in the jit.  It's only really faster using SSSE3 (on my desktop) for vc2i.  vuc2i is a wash, but at least it should be less bytes of code.  It was slower for vs2i/vus2i (which makes sense, those are awfully simple.)

-[Unknown]