spi_flash: Making XMC flash works more stable when brownout detected

components/bootloader_support/bootloader_flash/include/bootloader_flash.h

@@ -49,6 +49,12 @@ esp_err_t bootloader_flash_xmc_startup(void);
   */
 esp_err_t  __attribute__((weak)) bootloader_flash_unlock(void);
 
+/**
+ * @brief Reset the flash chip (66H + 99H).
+ *
+ * @return ESP_OK if success, otherwise ESP_FAIL.
+ */
+esp_err_t bootloader_flash_reset_chip(void);
 
 #ifdef __cplusplus
 }