Fix jump/call alignment, no-pos vertices

http://forums.ppsspp.org/showthread.php?tid=1276&pid=82633#pid82633

According to my tests, CALL and JUMP simply ignore the bottom 2 bits, which isn't really that unusual.

I've also verified that PRIM does not modify VADDR/IADDR, although it does of course return the context addr (from sceGeSaveContext.)

While testing that, I tested vertextype = 0.  This has a width of 3 bytes, and is afaict treated basically like s8 positions are.  I know there were some experiments with that in the past, but posalign/possize were always 0 then, and I think the steps were too.

-[Unknown]