binman: Add an FDT map

An FDT map is an entry which holds a full description of the image
entries, in FDT format. It can be discovered using the magic string at
its start. Tools can locate and read this entry to find out what entries
are in the image and where each entry is located.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/README.entries b/tools/binman/README.entries
index 3241bef..7014d36 100644
--- a/tools/binman/README.entries
+++ b/tools/binman/README.entries
@@ -223,6 +223,44 @@
 
 
 
+Entry: fdtmap: An entry which contains an FDT map
+-------------------------------------------------
+
+Properties / Entry arguments:
+    None
+
+An FDT map is just a header followed by an FDT containing a list of all the
+entries in the image.
+
+The header is the string _FDTMAP_ followed by 8 unused bytes.
+
+When used, this entry will be populated with an FDT map which reflects the
+entries in the current image. Hierarchy is preserved, and all offsets and
+sizes are included.
+
+Note that the -u option must be provided to ensure that binman updates the
+FDT with the position of each entry.
+
+Example output for a simple image with U-Boot and an FDT map:
+
+/ {
+    size = <0x00000112>;
+    image-pos = <0x00000000>;
+    offset = <0x00000000>;
+    u-boot {
+        size = <0x00000004>;
+        image-pos = <0x00000000>;
+        offset = <0x00000000>;
+    };
+    fdtmap {
+        size = <0x0000010e>;
+        image-pos = <0x00000004>;
+        offset = <0x00000004>;
+    };
+};
+
+
+
 Entry: files: Entry containing a set of files
 ---------------------------------------------