deep_sleep: on S2 disable the brown out detector before deep sleeping

On S2 the brown out detector would occasionally trigger erroneously during deep sleep.

Disable it before sleeping to circumvent this issue.

Closes https://github.com/espressif/esp-idf/issues/6179

components/esp32c3/include/esp32c3/brownout.h

@@ -1,4 +1,4 @@
-// Copyright 2015-2020 Espressif Systems (Shanghai) PTE LTD
+// Copyright 2015-2021 Espressif Systems (Shanghai) PTE LTD
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -16,6 +16,16 @@
 #ifndef __ESP_BROWNOUT_H
 #define __ESP_BROWNOUT_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 void esp_brownout_init(void);
 
+void esp_brownout_disable(void);
+
+#ifdef __cplusplus
+}
+#endif
+
 #endif