stm32_flash:Need conditinal on non F4 targets

arch/arm/src/stm32/stm32_flash.c

@@ -128,6 +128,7 @@ static void flash_lock(void)
   modifyreg32(STM32_FLASH_CR, 0, FLASH_CR_LOCK);
 }
 
+#if defined(CONFIG_STM32_FLASH_WORKAROUND_DATA_CACHE_CORRUPTION_ON_RWW)
 static void data_cache_disable(void)
 {
   modifyreg32(STM32_FLASH_ACR, FLASH_ACR_DCEN, 0);
@@ -143,6 +144,7 @@ static void data_cache_enable(void)
 
   modifyreg32(STM32_FLASH_ACR, 0, FLASH_ACR_DCEN);
 }
+#endif
 
 /************************************************************************************
  * Public Functions