[NUCLEO_F401RE] Add auto clock configuration (HSE/HSI)

Solve also the problem with the SetSysClock function not declared in
sleep.c

Conflicts:
	libraries/mbed/targets/hal/TARGET_STM/TARGET_NUCLEO_F401RE/i2c_api.c

Author: bcostm

libraries/mbed/targets/cmsis/TARGET_STM/TARGET_NUCLEO_F401RE/stm32f4xx_hal_conf.h

@@ -103,7 +103,7 @@
 #endif /* HSE_VALUE */
 
 #if !defined  (HSE_STARTUP_TIMEOUT)
-  #define HSE_STARTUP_TIMEOUT    ((uint32_t)50)   /*!< Time out for HSE start up, in ms */
+  #define HSE_STARTUP_TIMEOUT    ((uint32_t)100)   /*!< Time out for HSE start up, in ms */
 #endif /* HSE_STARTUP_TIMEOUT */
 
 /**
@@ -129,7 +129,7 @@
   *        frequency, this source is inserted directly through I2S_CKIN pad. 
   */
 #if !defined  (EXTERNAL_CLOCK_VALUE)
-  #define EXTERNAL_CLOCK_VALUE    ((uint32_t)12288000) /*!< Value of the Internal oscillator in Hz*/
+  #define EXTERNAL_CLOCK_VALUE    ((uint32_t)12288000) /*!< Value of the external oscillator in Hz*/
 #endif /* EXTERNAL_CLOCK_VALUE */
 
 /* Tip: To avoid modifying this file each time you need to use different HSE,