binman: Add a way to read the ROM offset

Provide a function to read the ROM offset so that we can store the value
in one place and clients don't need to store it themselves after calling
binman_set_rom_offset().

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/binman.h b/include/binman.h
index e0b9207..8b89a96 100644
--- a/include/binman.h
+++ b/include/binman.h
@@ -43,6 +43,13 @@
 void binman_set_rom_offset(int rom_offset);
 
 /**
+ * binman_get_rom_offset() - Get the ROM memory-map offset
+ *
+ * @returns offset from an image_pos to the memory-mapped address
+ */
+int binman_get_rom_offset(void);
+
+/**
  * binman_entry_find() - Find a binman symbol
  *
  * This searches the binman information in the device tree for a symbol of the