pseries: Update SLOF firmware image

It's been a while. This fixes compile warning, typos and
a bug with virtio-serial being used after it was shutdown
at "quiesce".

The full changelog is here:

Alexey Kardashevskiy (2):
      Remove ?PICK
      version: update to 20230918

Jordan Niethe (1):
      virtio-serial: Do not close stdout on quiesce

Kautuk Consul (1):
      virtio-serial: Make read and write methods report failure

Thomas Huth (10):
      lib/libnet/ipv6: Silence compiler warning from Clang
      Fix typos in the board-qemu folder
      Fix typos in the lib/libnet folder
      Fix typos in the remaining lib folders
      Fix typos in the slof folder
      Fix typos in the board-js2x folder
      Fix typos in the llfw folder
      Fix typos in the board-js2x folder
      Fix typos in the clients folder
      Fix remaining typos in various folders

Compiled with gcc-12.1.0-nolibc

Tested with (sorry, no KVM):

/home/aik/b/q-slof/qemu-system-ppc64 \
-nodefaults \
-chardev stdio,id=STDIO0,signal=off,mux=on \
-device spapr-vty,id=svty0,reg=0x71000110,chardev=STDIO0 \
-mon id=MON0,chardev=STDIO0,mode=readline \
-nographic \
-vga none \
-m 2G \
-kernel /home/aik/t/vml4150le \
-initrd /home/aik/t/le.cpio \
-machine pseries,cap-cfpc=broken,cap-sbbc=broken,cap-ibs=broken,cap-ccf-assist=off \
-bios pc-bios/slof.bin \
-trace events=/home/aik/qemu_trace_events \
-d guest_errors \
-chardev socket,id=SOCKET0,server=on,wait=off,path=qemu.mon.604650 \
-mon chardev=SOCKET0,mode=control \
-name 604650,debug-threads=on

[ npiggin: Also tested with KVM, including with virtio-console. ]

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

pc-bios/README

@@ -14,7 +14,7 @@
 - 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-20220719.
+  built from git tag qemu-slof-20230918.
 
 - VOF (Virtual Open Firmware) is a minimalistic firmware to work with
   -machine pseries,x-vof=on. When enabled, the firmware acts as a slim shim and