i965/vec4: Don't fix-up scalar uniforms for 3 src instructions.

Removes unnecessary MOV instructions in L4D2, TF2, Dota2, and many other
Steam games.

total instructions in shared programs: 1668126 -> 1657509 (-0.64%)
instructions in affected programs:     242235 -> 231618 (-4.38%)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp

@@ -277,6 +277,9 @@ vec4_visitor::fix_3src_operand(src_reg src)
    if (src.file != UNIFORM && src.file != IMM)
       return src;
 
+   if (src.file == UNIFORM && brw_is_single_value_swizzle(src.swizzle))
+      return src;
+
    dst_reg expanded = dst_reg(this, glsl_type::vec4_type);
    expanded.type = src.type;
    emit(MOV(expanded, src));