STM32: AnalogOut: do not call HAL_DAC_Start in dac_write

dac_write (used by AnalogOut.write) calls HAL_DAC_Start
every time. It is required to call HAL_DAC_Start only once.
HAL_DAC_Start uses internally HAL_Delay(1) making AnalogOut
not suitable for use in high speed application.
This change removes call to HAL_DAC_Start in dac_write and
moves it to analogout_init.

targets/TARGET_STM/TARGET_STM32F0/analogout_device.c

@@ -74,6 +74,7 @@ void analogout_init(dac_t *obj, PinName pin)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_free(dac_t *obj)

targets/TARGET_STM/TARGET_STM32F1/analogout_device.c

@@ -86,6 +86,7 @@ void analogout_init(dac_t *obj, PinName pin)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_free(dac_t *obj)

targets/TARGET_STM/TARGET_STM32F2/analogout_device.c

@@ -86,6 +86,7 @@ void analogout_init(dac_t *obj, PinName pin)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_free(dac_t *obj)

targets/TARGET_STM/TARGET_STM32F3/analogout_device.c

@@ -121,6 +121,7 @@ static void _analogout_init_direct(dac_t *obj, const PinMap *pinmap)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_init(dac_t *obj, PinName pin)

targets/TARGET_STM/TARGET_STM32F4/analogout_device.c

@@ -81,6 +81,7 @@ static void _analogout_init_direct(dac_t *obj, const PinMap *pinmap)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_init(dac_t *obj, PinName pin)

targets/TARGET_STM/TARGET_STM32F7/analogout_device.c

@@ -86,6 +86,7 @@ void analogout_init(dac_t *obj, PinName pin)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_free(dac_t *obj)

targets/TARGET_STM/TARGET_STM32G0/analogout_device.c

@@ -90,6 +90,7 @@ static void _analogout_init_direct(dac_t *obj, const PinMap *pinmap)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_init(dac_t *obj, PinName pin)

targets/TARGET_STM/TARGET_STM32G4/analogout_device.c

@@ -109,6 +109,7 @@ static void _analogout_init_direct(dac_t *obj, const PinMap *pinmap)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_init(dac_t *obj, PinName pin)

targets/TARGET_STM/TARGET_STM32H7/analogout_device.c

@@ -74,6 +74,7 @@ void analogout_init(dac_t *obj, PinName pin)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_free(dac_t *obj)

targets/TARGET_STM/TARGET_STM32L0/analogout_device.c

@@ -90,6 +90,7 @@ static void _analogout_init_direct(dac_t *obj, const PinMap *pinmap)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_init(dac_t *obj, PinName pin)

targets/TARGET_STM/TARGET_STM32L1/analogout_device.c

@@ -81,6 +81,7 @@ void analogout_init(dac_t *obj, PinName pin)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_free(dac_t *obj)

targets/TARGET_STM/TARGET_STM32L4/analogout_device.c

@@ -97,6 +97,7 @@ static void _analogout_init_direct(dac_t *obj, const PinMap *pinmap)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 
     /* DAC cannot be used in deepsleep/STOP mode */
     sleep_manager_lock_deep_sleep();

targets/TARGET_STM/TARGET_STM32L5/analogout_device.c

@@ -94,6 +94,7 @@ static void _analogout_init_direct(dac_t *obj, const PinMap *pinmap)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_init(dac_t *obj, PinName pin)

targets/TARGET_STM/TARGET_STM32WL/analogout_device.c

@@ -80,6 +80,7 @@ static void _analogout_init_direct(dac_t *obj, const PinMap *pinmap)
     }
 
     analogout_write_u16(obj, 0);
+    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_init(dac_t *obj, PinName pin)

targets/TARGET_STM/analogout_api.c

@@ -41,7 +41,6 @@
 static inline void dac_write(dac_t *obj, int value)
 {
     HAL_DAC_SetValue(&obj->handle, obj->channel, DAC_ALIGN_12B_R, (value & DAC_RANGE));
-    HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 static inline int dac_read(dac_t *obj)