Make G26 work with all mesh leveling.

Example Configuration.h files are not updated yet.   You need to cross
your settings over to the default Configuration.h file in the \Marlin
directory.   (UBL_G26_MESH_VALIDATION enablement has moved to a new
location in the file.)

Marlin/ultralcd.cpp

@@ -57,6 +57,10 @@
   extern void mesh_probing_done();
 #endif
 
+#if ENABLED(AUTO_BED_LEVELING_UBL) || ENABLED(G26_MESH_VALIDATION)
+  bool lcd_external_control;
+#endif
+
 // Initialized by settings.load()
 int16_t lcd_preheat_hotend_temp[2], lcd_preheat_bed_temp[2], lcd_preheat_fan_speed[2];
 
@@ -4603,8 +4607,8 @@ void lcd_update() {
 
     lcd_buttons_update();
 
-    #if ENABLED(AUTO_BED_LEVELING_UBL)
-      const bool UBL_CONDITION = !ubl.has_control_of_lcd_panel;
+    #if ENABLED(AUTO_BED_LEVELING_UBL) || ENABLED(G26_MESH_VALIDATION)
+      const bool UBL_CONDITION = lcd_external_control;
     #else
       constexpr bool UBL_CONDITION = true;
     #endif
@@ -5071,7 +5075,7 @@ void lcd_reset_alert_level() { lcd_status_message_level = 0; }
         case encrot3: ENCODER_SPIN(encrot2, encrot0); break;
       }
       #if ENABLED(AUTO_BED_LEVELING_UBL)
-        if (ubl.has_control_of_lcd_panel) {
+        if (lcd_external_control) {
           ubl.encoder_diff = encoderDiff;   // Make the encoder's rotation available to G29's Mesh Editor
           encoderDiff = 0;                  // We are going to lie to the LCD Panel and claim the encoder
                                             // knob has not turned.
@@ -5087,8 +5091,7 @@ void lcd_reset_alert_level() { lcd_status_message_level = 0; }
     bool lcd_detected() { return true; }
   #endif
 
-  #if ENABLED(AUTO_BED_LEVELING_UBL)
-
+  #if ENABLED(AUTO_BED_LEVELING_UBL) || ENABLED(G26_MESH_VALIDATION)
     void chirp_at_user() {
       #if ENABLED(LCD_USE_I2C_BUZZER)
         lcd.buzz(LCD_FEEDBACK_FREQUENCY_DURATION_MS, LCD_FEEDBACK_FREQUENCY_HZ);