bootloader_support: Rename include_priv directory to include_bootloader

Old rationale for "priv" no longer applies.

As reported here: https://esp32.com/viewtopic.php?f=13&t=6155&p=27151#p26601

components/bootloader_support/include_bootloader/bootloader_init.h

@@ -0,0 +1,28 @@
+// Copyright 2018 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 "esp_err.h"
+
+/* @brief Prepares hardware for work.
+ *
+ * Setting up:
+ * - Disable Cache access for both CPUs;
+ * - Initialise cache mmu;
+ * - Setting up pins and mode for SD, SPI, UART, Clocking.
+
+ *  @return ESP_OK   - If the setting is successful.
+ *          ESP_FAIL - If the setting is not successful.
+ */
+esp_err_t bootloader_init();