nir/GCM: Pull unpinned instructions out of blocks while pinning
nir/GCM: Pull unpinned instructions out of blocks while pinning

This lets us be slightly more efficient by not walking the CFG extra times.
Also, it may make it easier to ensure that GVN happens on only unpinned
instructions.

Reviewed-by: Reviewed-by: Connor Abbott <71178acffcc112b21e5858656e5751f5e4aa9364@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler