added defines for min and max steps per unit for E calibration

Firmware/variants/1_75mm_MK2-RAMBo13a-E3Dv6full.h

@@ -325,5 +325,7 @@ THERMISTORS SETTINGS
 
 #define STACK_GUARD_TEST_VALUE 0xA2A2
 
+#define MAX_E_STEPS_PER_UNIT 250
+#define MIN_E_STEPS_PER_UNIT 100
 
 #endif //__CONFIGURATION_PRUSA_H