Analogin: Add analogin_free() function to HAL

Author: mprse

hal/analogin_api.h

@@ -38,6 +38,7 @@ typedef struct analogin_s analogin_t;
  *
  * # Defined behaviour
  * * The function ::analogin_init initializes the analogin_t control structure
+ * * The function ::analogin_free returns the pin owned by the Analogin object to its reset state
  * * The function ::analogin_read reads the input voltage, represented as a float in the range [0.0 (GND), 1.0 (VCC)]
  * * The function ::analogin_read_u16 reads the value from analogin pin, represented as an unsigned 16bit value [0.0 (GND), MAX_UINT16 (VCC)]
  * * The accuracy of the ADC is +/- 10%
@@ -68,6 +69,13 @@ typedef struct analogin_s analogin_t;
  */
 void analogin_init(analogin_t *obj, PinName pin);
 
+/** Release the analogin peripheral
+ *
+ * Releases the pin used by analogin.
+ * @param obj The analogin object to initialize
+ */
+void analogin_free(analogin_t *obj);
+
 /** Read the input voltage, represented as a float in the range [0.0, 1.0]
  *
  * @param obj The analogin object