[fdt] Add the concept of an FDT image

Define the concept of an "FDT" image, representing a Flattened Device
Tree blob that has been downloaded in order to be provided to a kernel
or other executable image.  FDT images are represented using an image
tag (as with other special-purpose images such as the UEFI shim), and
are similarly marked as hidden so that they will not be included in a
generated magic initrd or show up in a virtual filesystem directory
listing.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/fdt.h

@@ -10,6 +10,7 @@
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <stdint.h>
+#include <ipxe/image.h>
 
 struct net_device;
 
@@ -93,6 +94,8 @@ struct fdt {
 	size_t strings_len;
 };
 
+extern struct image_tag fdt_image __image_tag;
+
 extern int fdt_path ( const char *path, unsigned int *offset );
 extern int fdt_alias ( const char *name, unsigned int *offset );
 extern const char * fdt_string ( unsigned int offset, const char *name );

src/include/usr/fdtmgmt.h

@@ -0,0 +1,16 @@
+#ifndef _USR_FDTMGMT_H
+#define _USR_FDTMGMT_H
+
+/** @file
+ *
+ * Flattened Device Tree management
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/image.h>
+
+extern int imgfdt ( struct image *image );
+
+#endif /* _USR_FDTMGMT_H */