AnalogIn for nRF51 Fixes

multiinstances was not suported for nrf51
made nrf_saadc SDK hal private for nRF52

hal/targets/hal/TARGET_NORDIC/TARGET_NRF5/TARGET_MCU_NRF51822/analogin_api.c

@@ -53,7 +53,7 @@ void analogin_init(analogin_t *obj, PinName pin)
     ret_code_t ret_code;
                                               // p_config, event_handler
     ret_code = nrf_drv_adc_init(NULL , NULL); // select blocking mode
-    MBED_ASSERT(ret_code == NRF_SUCCESS);
+    MBED_ASSERT((ret_code == NRF_SUCCESS) || (ret_code == NRF_ERROR_INVALID_STATE)); //NRF_ERROR_INVALID_STATE expected for multiple channels used.
 }
 
 uint16_t analogin_read_u16(analogin_t *obj)

hal/targets/hal/TARGET_NORDIC/TARGET_NRF5/sdk/drivers_nrf/hal/nrf_saadc.c

@@ -10,6 +10,7 @@
  *
  */
 
+#ifdef NRF52
 /**
  * @file
  * @brief SAADC HAL implementation
@@ -29,3 +30,6 @@ void nrf_saadc_channel_init(uint8_t channel, nrf_saadc_channel_config_t const *
     nrf_saadc_channel_input_set(channel, config->pin_p, config->pin_n);
     return;
 }
+
+#endif //NRF52
+

hal/targets/hal/TARGET_NORDIC/TARGET_NRF5/sdk/drivers_nrf/hal/nrf_saadc.h

@@ -14,6 +14,8 @@
 #ifndef NRF_SAADC_H_
 #define NRF_SAADC_H_
 
+#ifdef NRF52
+
 /**
  * @defgroup nrf_saadc_hal SAADC HAL
  * @{
@@ -27,6 +29,8 @@
 #include "nrf.h"
 #include "nrf_assert.h"
 
+
+
 #define NRF_SAADC_CHANNEL_COUNT 8
 
 /**
@@ -550,5 +554,7 @@ void nrf_saadc_channel_init(uint8_t channel, nrf_saadc_channel_config_t const *
 /**
  *@}
  **/
+ 
+#endif //  NRF52
 
 #endif /* NRF_SAADC_H_ */