Add support for 39sf020

Corresponding to coreboot v1 svn r523.
diff --git a/flash.h b/flash.h
index 1828176..2e1f600 100644
--- a/flash.h
+++ b/flash.h
@@ -27,6 +27,7 @@
 #define SST_ID            0xBF	/* SST Manufacturer ID[B code	*/
 #define SST_29EE020A      0x10	/* SST 29EE020 device code	*/
 #define SST_28SF040       0x04    /* SST 29EE040 device code	*/
+#define SST_39SF020       0xB6    /* SST 39SF020  device        */
 
 #define WINBOND_ID        0xDA	/* Winbond Manufacture ID code	*/
 #define W_29C020C         0x45	/* Winbond w29c020c device code*/
@@ -35,6 +36,10 @@
 extern int erase_28sf040 (struct flashchip * flash);
 extern int write_28sf040 (struct flashchip * flash, char * buf);
 
+extern int probe_39sf020 (struct flashchip * flash);
+extern int erase_39sf020 (struct flashchip * flash);
+extern int write_39sf020 (struct flashchip * flash, char * buf);
+
 extern int probe_29f040b (struct flashchip * flash);
 extern int erase_29f040b (struct flashchip * flash);
 extern int write_29f040b (struct flashchip * flash, char * buf);