ppc64: Fix out-of-tree builds

On ppc64 host, recursion into pc-bios/spapr-rtas/ fails for
out-of-tree builds. Add missing dir and symlink.

Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Alexander Graf <agraf@suse.de>
Signed-off-by: NAndreas Färber <andreas.faerber@web.de>
Signed-off-by: NAlexander Graf <agraf@suse.de>

configure

@@ -3475,11 +3475,13 @@ done # for target in $targets
 
 # build tree in object directory in case the source is not in the current directory
 DIRS="tests tests/cris slirp audio block net pc-bios/optionrom"
+DIRS="$DIRS pc-bios/spapr-rtas"
 DIRS="$DIRS roms/seabios roms/vgabios"
 DIRS="$DIRS fsdev ui"
 FILES="Makefile tests/Makefile"
 FILES="$FILES tests/cris/Makefile tests/cris/.gdbinit"
 FILES="$FILES pc-bios/optionrom/Makefile pc-bios/keymaps"
+FILES="$FILES pc-bios/spapr-rtas/Makefile"
 FILES="$FILES roms/seabios/Makefile roms/vgabios/Makefile"
 for bios_file in $source_path/pc-bios/*.bin $source_path/pc-bios/*.rom $source_path/pc-bios/*.dtb $source_path/pc-bios/openbios-*; do
     FILES="$FILES pc-bios/`basename $bios_file`"