Add board MKS_BASE_HEROIC (#9926)

Followup to #9008

- Don't define micro-stepping pins for boards that lack them.
- Allow setting of 128 microsteps with `M350`.

Marlin/src/pins/pins.h

@@ -102,6 +102,8 @@
   #include "pins_BAM_DICE_DUE.h"      // ATmega1280, ATmega2560
 #elif MB(MKS_BASE)
   #include "pins_MKS_BASE.h"          // ATmega1280, ATmega2560
+#elif MB(MKS_BASE_HEROIC)
+  #include "pins_MKS_BASE_HEROIC.h"   // ATmega1280, ATmega2560
 #elif MB(MKS_13)
   #include "pins_MKS_13.h"            // ATmega1280, ATmega2560
 #elif MB(MKS_GEN_L)