support for file based and sd partition based emusd

bdk/storage/file_based_storage.h

@@ -0,0 +1,15 @@
+#ifndef _FILE_BASED_STORAGE_H
+#define _FILE_BASED_STORAGE_H
+
+#include <bdk.h>
+
+
+int file_based_storage_init(const char *base_path);
+void file_based_storage_end();
+
+int file_based_storage_read(u32 sector, u32 num_sectors, void *buf);
+int file_based_storage_write(u32 sector, u32 num_sectors, void *buf);
+
+u32 file_based_storage_get_total_size();
+
+#endif