binman: Adjust naming for reading symbols

These functions get the value of a symbol. The reference to ELF files
is confusing since they are reading the position/size of entries, not
ELF symbols. Rename the functions and adjust the comments also.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/elf_test.py b/tools/binman/elf_test.py
index b641341..2f22639 100644
--- a/tools/binman/elf_test.py
+++ b/tools/binman/elf_test.py
@@ -37,7 +37,7 @@
     """A fake Section object, used for testing
 
     This has the minimum feature set needed to support testing elf functions.
-    A LookupSymbol() function is provided which returns a fake value for amu
+    A GetSymbolValue() function is provided which returns a fake value for any
     symbol requested.
     """
     def __init__(self, sym_value=1):
@@ -46,7 +46,7 @@
     def GetPath(self):
         return 'section_path'
 
-    def LookupImageSymbol(self, name, weak, msg, base_addr):
+    def GetImageSymbolValue(self, name, weak, msg, base_addr):
         """Fake implementation which returns the same value for all symbols"""
         return self.sym_value