bt: call nvs_flash_init in examples, show error if NVS is not initialized

NVS is used to store PHY calibration data, WiFi configuration, and BT
configuration. Previously BT examples did not call nvs_flash_init,
relying on the fact that it is called during PHY init. However PHY init
did not handle possible NVS initialization errors.

This change moves PHY init procedure into the application, and adds
diagnostic messages to BT config management routines if NVS is not
initialized.

examples/bluetooth/gatt_client/main/gattc_demo.c

@@ -24,6 +24,8 @@
 #include <string.h>
 #include <stdbool.h>
 #include <stdio.h>
+#include "nvs.h"
+#include "nvs_flash.h"
 #include "controller.h"
 
 #include "bt.h"
@@ -409,6 +411,14 @@ void gattc_client_test(void)
 
 void app_main()
 {
+    // Initialize NVS.
+    esp_err_t ret = nvs_flash_init();
+    if (ret == ESP_ERR_NVS_NO_FREE_PAGES) {
+        ESP_ERROR_CHECK(nvs_flash_erase());
+        ret = nvs_flash_init();
+    }
+    ESP_ERROR_CHECK( ret );
+
     esp_bt_controller_config_t bt_cfg = BT_CONTROLLER_INIT_CONFIG_DEFAULT();
     esp_bt_controller_init(&bt_cfg);
     esp_bt_controller_enable(ESP_BT_MODE_BTDM);