pseries: Update SLOF firmware image to qemu-slof-20150429

The changelog is:
  > version: update to 20150429
  > pci: Use QEMU created PCI device nodes
  > usb: support 64-bit pci bars
  > pci: Support 64-bit address translation
  > pci: program correct bridge limit registers during probe
  > scsi: handle report-luns failure
  > Fix "key?" Forth word when using USB keyboards
  > Remove bulk.fs package
  > Include make.rules in the library Makefiles

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Alexander Graf <agraf@suse.de>
