Add dedicated chip erase function for SST49LF040

Corresponding to flashrom svn r31 and coreboot v2 svn r1852.
diff --git a/sst49lf040.h b/sst49lf040.h
index 9e3cfa4..79dfec9 100644
--- a/sst49lf040.h
+++ b/sst49lf040.h
@@ -1,6 +1,7 @@
 #ifndef __SST49LF040_H__
 #define __SST49LF040_H__ 1
 
+extern int erase_49lf040(struct flashchip *flash);
 extern int write_49lf040(struct flashchip *flash, unsigned char *buf);
 
 #endif				/* !__SST49LF040_H__ */