Swap F4x1 default board files away from blackpill (#17522)

builddefs/mcu_selection.mk

@@ -359,7 +359,7 @@ ifneq ($(findstring STM32F401, $(MCU)),)
 
   # Board: it should exist either in <chibios>/os/hal/boards/,
   # <keyboard_dir>/boards/, or drivers/boards/
-  BOARD ?= BLACKPILL_STM32_F401
+  BOARD ?= GENERIC_STM32_F401XC
 
   USE_FPU ?= yes
 
@@ -475,7 +475,7 @@ ifneq ($(findstring STM32F411, $(MCU)),)
 
   # Board: it should exist either in <chibios>/os/hal/boards/,
   # <keyboard_dir>/boards/, or drivers/boards/
-  BOARD ?= BLACKPILL_STM32_F411
+  BOARD ?= GENERIC_STM32_F411XE
 
   USE_FPU ?= yes