binman: Add a function to decode an ELF file

Add a function which decodes an ELF file, working out where in memory each
part of the data should be written.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/README b/tools/binman/README
index 28624fa..0ff30ef 100644
--- a/tools/binman/README
+++ b/tools/binman/README
@@ -181,6 +181,10 @@
 Running binman
 --------------
 
+First install prerequisites, e.g.
+
+	sudo apt-get install python-pyelftools python3-pyelftools
+
 Type:
 
 	binman -b <board_name>