nir: add lowering for ffloor

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/nir/nir.h

@@ -2083,6 +2083,9 @@ typedef struct nir_shader_compiler_options {
     */
    bool fdot_replicates;
 
+   /** lowers ffloor to fsub+ffract: */
+   bool lower_ffloor;
+
    /** lowers ffract to fsub+ffloor: */
    bool lower_ffract;