Update OpenBIOS images to r683

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

pc-bios/README

@@ -14,8 +14,8 @@
 - OpenBIOS (http://www.openbios.org/) is a free (GPL v2) portable
   firmware implementation. The goal is to implement a 100% IEEE
   1275-1994 (referred to as Open Firmware) compliant firmware.
-  The included images for PowerPC (for 32 and 64 bit PPC CPUs) are built from
-  OpenBIOS SVN revision 640, Sparc64 images from r665 and Sparc32 from r666.
+  The included images for PowerPC (for 32 and 64 bit PPC CPUs),
+  Sparc32 and Sparc64 are built from OpenBIOS SVN revision 683.
 
 - The PXE roms come from Rom-o-Matic gPXE 0.9.9 with BANNER_TIMEOUT=0