pseries: Update SLOF

This patch updates the SLOF version, introducing a number of fixes:
 * add proper graphics support
 * fix bugs with graphical terminal under grub2
 * fix bugs in handling of 64-bit unit addresses
 * fix VSCSI representation to be closer to PowerVM
 * fix bugs which caused grub2 to crash

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>

pc-bios/README

@@ -17,7 +17,7 @@
 - SLOF (Slimline Open Firmware) is a free IEEE 1275 Open Firmware
   implementation for certain IBM POWER hardware.  The sources are at
   https://github.com/dgibson/SLOF, and the image currently in qemu is
-  built from git tag qemu-slof-20120217.
+  built from git tag qemu-slof-20120719.
 
 - sgabios (the Serial Graphics Adapter option ROM) provides a means for
   legacy x86 software to communicate with an attached serial console as