Add HAS_ROTARY_ENCODER

Marlin/src/inc/Conditionals_post.h

   #endif
 #endif
 
+#if BUTTONS_EXIST(EN1, EN2, ENC)
+  #define HAS_ROTARY_ENCODER 1
+#endif
+
 #if !NUM_SERIAL
   #undef BAUD_RATE_GCODE
 #elif NUM_SERIAL > 1