PPC: Add new target config for pseries

We only support -M pseries when certain prerequisites are met, such
as a PPC64 guest and libfdt. To only gather these requirements in
a single place, this patch introduces a new CONFIG_PSERIES variable
that gets set when all prerequisites are met.

Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/configure b/configure
index 59b1494..29cdd75 100755
--- a/configure
+++ b/configure
@@ -3389,6 +3389,9 @@
       fi
     fi
 esac
+if test "$target_arch2" = "ppc64" -a "$fdt" = "yes"; then
+  echo "CONFIG_PSERIES=y" >> $config_target_mak
+fi
 if test "$target_bigendian" = "yes" ; then
   echo "TARGET_WORDS_BIGENDIAN=y" >> $config_target_mak
 fi