STM32H7 : add LSI

Author: jeromecoutant

targets/TARGET_STM/TARGET_STM32H7/device/stm32h7xx_hal_conf.h

@@ -121,6 +121,15 @@
   #define HSI_VALUE    ((uint32_t)64000000) /*!< Value of the Internal oscillator in Hz*/
 #endif /* HSI_VALUE */
 
+/**
+  * @brief Internal Low Speed oscillator (LSI) value.
+  */
+#if !defined  (LSI_VALUE)
+ #define LSI_VALUE  32000U                  /*!< LSI Typical Value in Hz*/
+#endif /* LSI_VALUE */                      /*!< Value of the Internal Low Speed oscillator in Hz
+                                             The real value may vary depending on the variations
+                                             in voltage and temperature.  */
+
 /**
   * @brief External Low Speed oscillator (LSE) value.
   *        This value is used by the UART, RTC HAL module to compute the system frequency