feat: add user data to bin header

user could put some data into bin header by USER_DATA_ATTR attribute, defined in esp_attr.h

components/esp8266/include/esp_attr.h

@@ -46,4 +46,7 @@
 // Forces read-only data into RTC memory.
 #define RTC_RODATA_ATTR __attribute__((section(".rtc.rodata")))
 
+// Forces to put some user defined data in the binary file header, the offset is 0x10.
+#define USER_DATA_ATTR __attribute__((section(".user.data")))
+
 #endif /* __ESP_ATTR_H__ */

components/esp8266/ld/esp8266.common.ld

@@ -230,6 +230,7 @@ SECTIONS
   .irom0.text : ALIGN(4)
   {
     _irom0_text_start = ABSOLUTE(.);
+    *(.user.data)
     *(.rodata.* .rodata .irom0.literal .irom.literal .irom.text.literal .irom0.text .irom.text)
     *(.literal.* .text.*)