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/esp32/include/esp32/brownout.h

@@ -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