Move M900 to cpp

Marlin/src/Marlin.cpp

   SYNC_PLAN_POSITION_KINEMATIC();
 }
 
-#if ENABLED(LIN_ADVANCE)
-  #include "gcode/feature/advance/M900.h"
-#endif
-
 #if ENABLED(HAVE_TMC2130)
   #include "feature/tmc2130.h"
   #include "gcode/feature/trinamic/M906.h"

Marlin/src/gcode/feature/advance/M900.h → Marlin/src/gcode/feature/advance/M900.cpp

  *
  */
 
+#include "../../../inc/MarlinConfig.h"
+
+#if ENABLED(LIN_ADVANCE)
+
+#include "../../gcode.h"
+#include "../../../module/planner.h"
+#include "../../../module/stepper.h"
+
 /**
  * M900: Set and/or Get advance K factor and WH/D ratio
  *
  *  R<ratio>                   Set ratio directly (overrides WH/D)
  *  W<width> H<height> D<diam> Set ratio from WH/D
  */
-void gcode_M900() {
+void GcodeSuite::M900() {
   stepper.synchronize();
 
   const float newK = parser.floatval('K', -1);
                 newW = parser.floatval('W', -1),
                 newH = parser.floatval('H', -1);
     if (newD >= 0 && newW >= 0 && newH >= 0)
-      newR = newD ? (newW * newH) / (sq(newD * 0.5) * M_PI) : 0;
+      newR = newD ? (newW * newH) / CIRCLE_AREA(newD * 0.5) : 0;
   }
   if (newR >= 0) planner.advance_ed_ratio = newR;
 
   if (ratio) SERIAL_ECHO(ratio); else SERIAL_ECHOPGM("Auto");
   SERIAL_EOL();
 }
+
+#endif // LIN_ADVANCE

Marlin/src/gcode/gcode.cpp

 extern void gcode_M350();
 extern void gcode_M351();
 extern void gcode_M355();
-extern void gcode_M900();
 extern void gcode_M906();
 extern void gcode_M911();
 extern void gcode_M912();
       #endif
 
       #if ENABLED(LIN_ADVANCE)
-        case 900: // M900: Set advance K factor.
-          gcode_M900();
-          break;
+        case 900: M900(); break;  // M900: Set advance K factor.
       #endif
 
       #if ENABLED(HAVE_TMC2130)