spi_flash: support working on differnt buses and frequency

components/spi_flash/include/spi_flash_chip_issi.h

@@ -0,0 +1,27 @@
+// Copyright 2015-2019 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>
+#include "esp_flash.h"
+#include "spi_flash_chip_driver.h"
+
+
+/**
+ * ISSI SPI flash chip_drv, uses all the above functions for its operations. In
+ * default autodetection, this is used as a catchall if a more specific chip_drv
+ * is not found.
+ */
+extern const spi_flash_chip_t esp_flash_chip_issi;