bootloader: Ensure bootloader never returns to caller

* Fixes some "noreturn" functions in bootloader utils which did return (causing fatal CPU
  exceptions).
* Marks bootloader entry as "noreturn", preventing "user code done" from stalling boot
  Partial fix for https://github.com/espressif/esp-idf/issues/1814 TW20016
  (Comprehensive fix for this issue will be enabling WDT during bootloader, coming shortly.)

components/bootloader_support/include_priv/bootloader_utility.h

@@ -52,3 +52,13 @@ int bootloader_utility_get_selected_boot_partition(const bootloader_state_t *bs)
  * @param[in] start_index The index from which the search for images begins.
  */
 __attribute__((noreturn)) void bootloader_utility_load_boot_image(const bootloader_state_t *bs, int start_index);
+
+
+/**
+ * @brief Software reset the ESP32
+ *
+ * Bootloader code should call this in the case that it cannot proceed.
+ *
+ * It is not recommended to call this function from an app (if called, the app will abort).
+ */
+__attribute__((noreturn)) void bootloader_reset(void);