i965/vec4: use vec4_builder to emit instructions in setup_imm_df()

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
[ Francisco Jerez: Drop useless vec4_visitor dependencies.  Demote to
  static stand-alone function.  Don't write unused components in the
  result.  Use vec4_builder interface for register allocation. ]
Reviewed-by: Francisco Jerez <currojerez@riseup.net>

src/intel/compiler/brw_vec4.h

@@ -28,6 +28,7 @@
 
 #ifdef __cplusplus
 #include "brw_ir_vec4.h"
+#include "brw_vec4_builder.h"
 #endif
 
 #include "compiler/glsl/ir.h"
@@ -324,8 +325,6 @@ public:
    void emit_conversion_from_double(dst_reg dst, src_reg src, bool saturate);
    void emit_conversion_to_double(dst_reg dst, src_reg src, bool saturate);
 
-   src_reg setup_imm_df(double v);
-
    vec4_instruction *shuffle_64bit_data(dst_reg dst, src_reg src,
                                         bool for_write,
                                         bblock_t *block = NULL,