feat(esp8266): Add reset reason function

The function can be disable.

components/esp8266/include/internal/esp_system_internal.h

@@ -0,0 +1,53 @@
+// Copyright 2018-2019 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.
+// You may obtain a copy of the License at
+
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define RTC_SYS_RAM_SIZE            256
+
+/**
+ * The size of structure must not be larger than 256 bytes and all member varible must be uint32_t type
+ */
+struct _rtc_sys_info {
+    uint32_t        hint;   // software reset reason
+};
+
+extern struct _rtc_sys_info rtc_sys_info;
+
+/**
+ * @brief  Internal function to get SoC reset reason at system initialization
+ */
+void esp_reset_reason_init(void);
+
+/**
+ * @brief  Internal function to set reset reason hint
+ *
+ * The hint is used do distinguish different reset reasons when software reset
+ * is performed.
+ *
+ * The hint is stored in RTC store register, RTC_RESET_CAUSE_REG.
+ *
+ * @param hint  Desired esp_reset_reason_t value for the real reset reason
+ */
+void esp_reset_reason_set_hint(esp_reset_reason_t hint);
+
+#ifdef __cplusplus
+}
+#endif