Always use fastmem for sw/lw offset from SP

At first I was thinking we should check SP maybe, but the likelyhood of it being wrong is pretty low now.  We could still validate it, but that seems like a lot of work.

Unfortunately, it doesn't help as much as I hoped on Android.  I think it was ~3% improvement in ClaDun.  On x64, the improvement was 23%, and 15% in another game (which crashed on my Android due to running out of VRAM.)

Of course, fastmem is still better (much better.)

-[Unknown]