🔨 BTT STM32G0B1RE xfer build (#24245)

Marlin/src/inc/SanityCheck.h

 #elif ENABLED(DISABLE_JTAG) && !defined(JTAG_DISABLE)
   #error "DISABLE_JTAG is not supported for the selected MCU/Board."
 #endif
+
+// Check requirements for upload.py
+#if ENABLED(XFER_BUILD) && !BOTH(BINARY_FILE_TRANSFER, CUSTOM_FIRMWARE_UPLOAD)
+  #error "BINARY_FILE_TRANSFER and CUSTOM_FIRMWARE_UPLOAD are required for custom upload."
+#endif

Marlin/src/pins/pins.h

 #elif MB(BTT_SKR_MINI_E3_V2_0)
   #include "stm32f1/pins_BTT_SKR_MINI_E3_V2_0.h"  // STM32F1                              env:STM32F103RC_btt env:STM32F103RC_btt_USB env:STM32F103RE_btt env:STM32F103RE_btt_USB env:STM32F103RC_btt_maple env:STM32F103RC_btt_USB_maple env:STM32F103RE_btt_maple env:STM32F103RE_btt_USB_maple
 #elif MB(BTT_SKR_MINI_E3_V3_0)
-  #include "stm32g0/pins_BTT_SKR_MINI_E3_V3_0.h"  // STM32G0                              env:STM32G0B1RE_btt
+  #include "stm32g0/pins_BTT_SKR_MINI_E3_V3_0.h"  // STM32G0                              env:STM32G0B1RE_btt env:STM32G0B1RE_btt_xfer
 #elif MB(BTT_SKR_MINI_MZ_V1_0)
   #include "stm32f1/pins_BTT_SKR_MINI_MZ_V1_0.h"  // STM32F1                              env:STM32F103RC_btt env:STM32F103RC_btt_USB env:STM32F103RC_btt_maple env:STM32F103RC_btt_USB_maple
 #elif MB(BTT_SKR_E3_DIP)

ini/stm32f1.ini

 #
 [STM32F103Rx_creality_xfer]
 extends         = STM32F103Rx_creality
+build_flags     = ${STM32F103Rx_creality.build_flags} -DXFER_BUILD
 extra_scripts   = ${STM32F103Rx_creality.extra_scripts}
                   pre:buildroot/share/scripts/upload.py
 upload_protocol = custom

ini/stm32g0.ini

                             -DSTEP_TIMER_IRQ_PRIO=0
 upload_protocol             = stlink
 debug_tool                  = stlink
+
+#
+# Custom upload to SD via Marlin with Binary Protocol
+#
+[env:STM32G0B1RE_btt_xfer]
+extends         = env:STM32G0B1RE_btt
+build_flags     = ${env:STM32G0B1RE_btt.build_flags} -DXFER_BUILD
+extra_scripts   = ${env:STM32G0B1RE_btt.extra_scripts}
+                  pre:buildroot/share/scripts/upload.py
+upload_protocol = custom