W25QXX SPI Flash support (#18897)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/gcode/gcode.cpp

@@ -871,6 +871,11 @@ void GcodeSuite::process_parsed_command(const bool no_ok/*=false*/) {
         case 422: M422(); break;                                  // M422: Set Z Stepper automatic alignment position using probe
       #endif
 
+      #if BOTH(HAS_SPI_FLASH, SDSUPPORT)
+        case 993: M993(); break;                                  // M993: Backup SPI Flash to SD
+        case 994: M994(); break;                                  // M994: Load a Backup from SD to SPI Flash
+      #endif
+
       #if ENABLED(TOUCH_SCREEN_CALIBRATION)
         case 995: M995(); break;                                  // M995: Touch screen calibration for TFT display
       #endif