glsl: Combine many instruction lowering passes into one.

This should save on the overhead of tree-walking and provide a
convenient place to add more instruction lowering in the future.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>

src/glsl/glsl_parser_extras.cpp

@@ -708,7 +708,7 @@ do_common_optimization(exec_list *ir, bool linked, unsigned max_unroll_iteration
 {
    GLboolean progress = GL_FALSE;
 
-   progress = do_sub_to_add_neg(ir) || progress;
+   progress = lower_instructions(ir, SUB_TO_ADD_NEG) || progress;
 
    if (linked) {
       progress = do_function_inlining(ir) || progress;