stm32 BSPs to support nano version (RT_USING_NANO) 这个commit支持到stm32f7之前的BSP
2. Bsp stm32l452-st-nucleo has been tested with NUCLEO-L452RE board. 3. Modify the applications SConscript of bsp stm32f103-yf-ufun, using new method. 4. Modify README of bsp stm32f072-st-nucleo.