Add support for 39sf020

Corresponding to coreboot v1 svn r523.
diff --git a/flash_rom.c b/flash_rom.c
index 0b7b768..171fe3e 100644
--- a/flash_rom.c
+++ b/flash_rom.c
@@ -47,6 +47,8 @@
      probe_jedec,   erase_jedec,   write_jedec},
     {"SST28SF040A", SST_ID,     SST_28SF040,  NULL, 512, 256,
      probe_28sf040, erase_28sf040, write_28sf040},
+    {"SST39SF020A", SST_ID,     SST_39SF020,  NULL, 256, 4096,
+     probe_jedec, erase_jedec, write_39sf020},
     {"W29C020C",    WINBOND_ID, W_29C020C,    NULL, 256, 128,
      probe_jedec,   erase_jedec,   write_jedec},
     {NULL,}