st/nine: Reorganize ff vtx processing
st/nine: Reorganize ff vtx processing

The new order simplified the code a bit for
next patches.

Signed-off-by: Axel Davy <2b6ef604b998fb81662f85c329e4fc020eae8e5d@ens.fr>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler