Move z_endstop_adj to Endstops

Marlin/src/Marlin.cpp

 millis_t max_inactive_time = 0,
          stepper_inactive_time = (DEFAULT_STEPPER_DEACTIVE_TIME) * 1000UL;
 
-#if ENABLED(Z_DUAL_ENDSTOPS)
-  float z_endstop_adj;
-#endif
-
 #if ENABLED(FILAMENT_RUNOUT_SENSOR)
   static bool filament_ran_out = false;
 #endif

Marlin/src/Marlin.h

 // Inactivity shutdown timer
 extern millis_t max_inactive_time, stepper_inactive_time;
 
-#if ENABLED(Z_DUAL_ENDSTOPS)
-  extern float z_endstop_adj;
-#endif
-
 #if HAS_SERVOS
   #include "HAL/servo.h"
   extern HAL_SERVO_LIB servo[NUM_SERVOS];

Marlin/src/gcode/calibrate/M666.cpp

 
 #elif ENABLED(Z_DUAL_ENDSTOPS) // !DELTA && ENABLED(Z_DUAL_ENDSTOPS)
 
-  #include "../../Marlin.h" // for z_endstop_adj
+  #include "../../module/endstops.h"
 
   /**
    * M666: For Z Dual Endstop setup, set z axis offset to the z2 axis.
    */
   void GcodeSuite::M666() {
-    if (parser.seen('Z')) z_endstop_adj = parser.value_linear_units();
-    SERIAL_ECHOLNPAIR("Z Endstop Adjustment set to (mm):", z_endstop_adj);
+    if (parser.seen('Z')) endstops.z_endstop_adj = parser.value_linear_units();
+    SERIAL_ECHOLNPAIR("Z Endstop Adjustment set to (mm):", endstops.z_endstop_adj);
   }
 
 #endif

Marlin/src/module/configuration_store.cpp

  *  ---  M665 Z    delta_tower_angle_trim[C]        (float) is always 0.0
  *
  * Z_DUAL_ENDSTOPS:                                 48 bytes
- *  348  M666 Z    z_endstop_adj                    (float)
+ *  348  M666 Z    endstops.z_endstop_adj           (float)
  *  ---            dummy data                       (float x11)
  *
  * ULTIPANEL:                                       6 bytes
       dummy = 0.0f;
       for (uint8_t q = 3; q--;) EEPROM_WRITE(dummy);
     #elif ENABLED(Z_DUAL_ENDSTOPS)
-      EEPROM_WRITE(z_endstop_adj);             // 1 float
+      EEPROM_WRITE(endstops.z_endstop_adj);    // 1 float
       dummy = 0.0f;
       for (uint8_t q = 11; q--;) EEPROM_WRITE(dummy);
     #else
         dummy = 0.0f;
         for (uint8_t q=3; q--;) EEPROM_READ(dummy);
       #elif ENABLED(Z_DUAL_ENDSTOPS)
-        EEPROM_READ(z_endstop_adj);
+        EEPROM_READ(endstops.z_endstop_adj);    // 1 float
         dummy = 0.0f;
         for (uint8_t q=11; q--;) EEPROM_READ(dummy);
       #else
 
   #elif ENABLED(Z_DUAL_ENDSTOPS)
 
-    z_endstop_adj =
+    endstops.z_endstop_adj =
       #ifdef Z_DUAL_ENDSTOPS_ADJUSTMENT
         Z_DUAL_ENDSTOPS_ADJUSTMENT
       #else
         SERIAL_ECHOLNPGM("Z2 Endstop adjustment:");
       }
       CONFIG_ECHO_START;
-      SERIAL_ECHOLNPAIR("  M666 Z", LINEAR_UNIT(z_endstop_adj));
+      SERIAL_ECHOLNPAIR("  M666 Z", LINEAR_UNIT(endstops.z_endstop_adj));
     #endif // DELTA
 
     #if ENABLED(ULTIPANEL)

Marlin/src/module/endstops.cpp

   volatile bool Endstops::z_probe_enabled = false;
 #endif
 
+#if ENABLED(Z_DUAL_ENDSTOPS)
+  float Endstops::z_endstop_adj;
+#endif
+
 /**
  * Class and Instance Methods
  */

Marlin/src/module/endstops.h

     static volatile char endstop_hit_bits; // use X_MIN, Y_MIN, Z_MIN and Z_MIN_PROBE as BIT value
 
     #if ENABLED(Z_DUAL_ENDSTOPS)
+      static float z_endstop_adj;
       typedef uint16_t esbits_t;
     #else
       typedef byte esbits_t;

Marlin/src/module/motion.cpp

 
   #if ENABLED(Z_DUAL_ENDSTOPS)
     if (axis == Z_AXIS) {
-      float adj = FABS(z_endstop_adj);
+      float adj = FABS(endstops.z_endstop_adj);
       bool lockZ1;
       if (axis_home_dir > 0) {
         adj = -adj;
-        lockZ1 = (z_endstop_adj > 0);
+        lockZ1 = (endstops.z_endstop_adj > 0);
       }
       else
-        lockZ1 = (z_endstop_adj < 0);
+        lockZ1 = (endstops.z_endstop_adj < 0);
 
       if (lockZ1) stepper.set_z_lock(true); else stepper.set_z2_lock(true);