vc4: Don't bother de-SSAing values that aren't part of phi webs.
vc4: Don't bother de-SSAing values that aren't part of phi webs.

We can just support them the same way we do load_const's SSA values.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler