configure: move SLOF submodule handling to pc-bios/s390-ccw

Move the handling of the roms/SLOF submodule out of the main Makefile,
since we are going to remove submodules from the build process of QEMU.

Acked-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/configure b/configure
index 45d43dd..de3904f 100755
--- a/configure
+++ b/configure
@@ -1662,7 +1662,8 @@
 
 # Only build s390-ccw bios if the compiler has -march=z900 or -march=z10
 # (which is the lowest architecture level that Clang supports)
-if have_target s390x-softmmu && probe_target_compiler s390x-softmmu; then
+if have_target s390x-softmmu && probe_target_compiler s390x-softmmu && \
+    GIT=git "$source_path/scripts/git-submodule.sh" "$git_submodules_action" roms/SLOF >> config.log 2>&1; then
   write_c_skeleton
   do_compiler "$target_cc" $target_cc_cflags -march=z900 -o $TMPO -c $TMPC
   has_z900=$?
@@ -1675,10 +1676,8 @@
     config_mak=pc-bios/s390-ccw/config-host.mak
     echo "# Automatically generated by configure - do not modify" > $config_mak
     echo "SRC_PATH=$source_path/pc-bios/s390-ccw" >> $config_mak
+    echo "GIT_SUBMODULES_ACTION=$git_submodules_action" >> $config_mak
     write_target_makefile >> $config_mak
-    # SLOF is required for building the s390-ccw firmware on s390x,
-    # since it is using the libnet code from SLOF for network booting.
-    git_submodules="${git_submodules} roms/SLOF"
   fi
 fi