i965: Make invalidate_live_intervals() a virtual method of backend_visitor.

Reviewed-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_shader.h

@@ -88,6 +88,8 @@ public:
    void dump_instructions();
 
    void assign_common_binding_table_offsets(uint32_t next_binding_table_offset);
+
+   virtual void invalidate_live_intervals() = 0;
 };
 
 uint32_t brw_texture_offset(struct gl_context *ctx, ir_constant *offset);