draw: fix front face injection

draw: fix front face injection

Inject front face only if the fragment shader uses it and
propagate through all channels because otherwise we'll
need to figure out the exact swizzle that the fs expects and
it's just simpler to make sure all the components within
the front face register are correctly set.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>