Add support for MKS Robin board (#12650)

Implement initial support for MKS Robin (STM32F103ZET6) board.
Custom build script is used to generate encrypted firmware compatible with original MSK Robin bootloader (i.e. safe firmware update from SD card and possibility to go back to original close-source firmware).

Marlin/src/pins/pins.h

@@ -392,6 +392,8 @@
   #include "pins_GTM32_PRO_VB.h"      // STM32F1                                    env:STM32F1
 #elif MB(MORPHEUS)
   #include "pins_MORPHEUS.h"          // STM32F1                                    env:STM32F1
+#elif MB(MKS_ROBIN)
+  #include "pins_MKS_ROBIN.h"         // STM32F1                                    env:STM32F1
 
 //
 // STM32 ARM Cortex-M4F