pseries: Update SLOF firmware image

This allocates space for FWNMI log in RTAS and fixes phandles at
the ibm,client-architecture-support stage.

The full list is:
 * libnet: Fix the check of the argument lengths of the "ping" command
 * fdt: Update phandles after H_CAS
 * rtas: Reserve space for FWNMI log

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

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-20190719.
+  built from git tag qemu-slof-20190827.
 
 - sgabios (the Serial Graphics Adapter option ROM) provides a means for
   legacy x86 software to communicate with an attached serial console as

SLOF @ ea221600

-Subproject commit 7bfe584e321946771692711ff83ad2b5850daca7
+Subproject commit ea221600a116883137ef90b2b7ab7d2472bc4f10