pseries: Update SLOF firmware image to qemu-slof-20140404

The change log is:
  > Isolate sc 1 detection logic
  > build: auto-detect ppc64 architecture
  > cas: increase hcall buffer size to accomodate 256 cpus
  > usb: change device tree naming
  > usb-core: adjust port numbers in set_address
  > virtio-scsi: correct srplun comment
  > Fix kernel loading
  > Workaround to make grub2 assign server ip from dhcp ack packet only
  > ELF: Enter LE binary in LE mode
  > ELF loading should fail for virt != phys
Signed-off-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: NAlexander 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/aik/SLOF, and the image currently in qemu is
-  built from git tag qemu-slof-20140304.
+  built from git tag qemu-slof-20140404.
 
 - sgabios (the Serial Graphics Adapter option ROM) provides a means for
   legacy x86 software to communicate with an attached serial console as

SLOF @ c90b50b5

-Subproject commit af6b7bf5879b6cd6825de2a107cb0e3219fb1df5
+Subproject commit c90b50b5055f976a0da3c032f26fb80157292adc