binman: Support finding symbols in sub-sections

At present binman only supports resolving symbols in the same section as
the binary that uses it. This is quite limited because we often need to
group entries into different sections.

Enhance the algorithm to search the entire image for symbols.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/elf.py b/tools/binman/elf.py
index 249074a..03b49d7 100644
--- a/tools/binman/elf.py
+++ b/tools/binman/elf.py
@@ -132,7 +132,8 @@
                                  (msg, sym.size))
 
             # Look up the symbol in our entry tables.
-            value = section.LookupSymbol(name, sym.weak, msg, base.address)
+            value = section.GetImage().LookupImageSymbol(name, sym.weak, msg,
+                                                         base.address)
             if value is None:
                 value = -1
                 pack_string = pack_string.lower()