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>
diff --git a/src/glsl/SConscript b/src/glsl/SConscript
index 4cb2d8b..f708635 100644
--- a/src/glsl/SConscript
+++ b/src/glsl/SConscript
@@ -49,14 +49,11 @@
     'loop_analysis.cpp',
     'loop_controls.cpp',
     'loop_unroll.cpp',
-    'lower_div_to_mul_rcp.cpp',
-    'lower_explog_to_explog2.cpp',
     'lower_if_to_cond_assign.cpp',
+    'lower_instructions.cpp',
     'lower_jumps.cpp',
     'lower_mat_op_to_vec.cpp',
-    'lower_mod_to_fract.cpp',
     'lower_noise.cpp',
-    'lower_sub_to_add_neg.cpp',
     'lower_variable_index_to_cond_assign.cpp',
     'lower_vec_index_to_cond_assign.cpp',
     'lower_vec_index_to_swizzle.cpp',