glsl: move variables in to ir_variable::data, part I

This patch moves following bitfields in to the data structure:

used, assigned, how_declared, mode, interpolation,
origin_upper_left, pixel_center_integer

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>

src/glsl/ir_constant_expression.cpp

@@ -1583,7 +1583,7 @@ ir_dereference_variable::constant_expression_value(struct hash_table *variable_c
    /* The constant_value of a uniform variable is its initializer,
     * not the lifetime constant value of the uniform.
     */
-   if (var->mode == ir_var_uniform)
+   if (var->data.mode == ir_var_uniform)
       return NULL;
 
    if (!var->constant_value)