[bsp][stm32f7]Fix "scons --dist" error in stm32f7's bsp

Signed-off-by: Willian Chan <chentingwei@rt-thread.com>

bsp/stm32/libraries/templates/stm32f7xx/SConstruct

@@ -36,6 +36,9 @@ Export('rtconfig')
 # prepare building environment
 objs = PrepareBuilding(env, RTT_ROOT, has_libcpu=False)
 
+stm32_library = 'STM32F7xx_HAL'
+rtconfig.BSP_LIBRARY_TYPE = stm32_library
+
 SDK_ROOT = os.path.abspath('./')
 
 # include drivers

bsp/stm32/stm32f767-st-nucleo/SConstruct

@@ -36,6 +36,9 @@ Export('rtconfig')
 # prepare building environment
 objs = PrepareBuilding(env, RTT_ROOT, has_libcpu=False)
 
+stm32_library = 'STM32F7xx_HAL'
+rtconfig.BSP_LIBRARY_TYPE = stm32_library
+
 SDK_ROOT = os.path.abspath('./')
 
 # include drivers

bsp/stm32/stm32f769-st-disco/SConstruct

@@ -36,6 +36,9 @@ Export('rtconfig')
 # prepare building environment
 objs = PrepareBuilding(env, RTT_ROOT, has_libcpu=False)
 
+stm32_library = 'STM32F7xx_HAL'
+rtconfig.BSP_LIBRARY_TYPE = stm32_library
+
 SDK_ROOT = os.path.abspath('./')
 
 # include drivers