Minor armjit optimizations, fix B/BL encoding

SetJumpTarget() wrote BL for B, and B for BL.  Luckily we were never using it in a way we cared.

Also, cut an instruction from "andi x, y, 0xFFFF" and cut some instructions from "slt x, y, 0".  Probably won't really help perf anywhere.

Technically, & (any solid uninterrupted sequence of bits) could be optimized, in ANDI2R also, I suppose.

-[Unknown]