- Rename WRITE_E_STEP for consistency

- Add BIT and TEST macros
- Add _APPLY_ macros to stepper.cpp to help with consolidation
- Consolidate code in stepper.cpp using macros
- Apply standards in stepper.cpp
- Use >= 0 instead of > -1 as a better semantic
- Replace DUAL_Y_CARRIAGE with Y_DUAL_STEPPER_DRIVERS

Marlin/Marlin.ino

@@ -47,8 +47,8 @@
   #endif
 #endif
 
-#if defined(DIGIPOTSS_PIN) && DIGIPOTSS_PIN > -1
-#include <SPI.h>
+#if HAS_DIGIPOTSS
+  #include <SPI.h>
 #endif
 
 #if defined(DIGIPOT_I2C)