missing chunk of HVM direct kernel boot patch

Found by Stefano, this chunk of the patch was never applied to
xen-unstable (commit 11dffa2359),
see http://marc.info/?l=qemu-devel&m=140471493425353&w=2.

Signed-off-by: Chunyan Liu <cyliu@suse.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/libxl_dm.c

@@ -527,6 +527,15 @@ static char ** libxl__build_device_model_args_new(libxl__gc *gc,
     if (b_info->type == LIBXL_DOMAIN_TYPE_HVM) {
         int ioemu_nics = 0;
 
+        if (b_info->kernel)
+            flexarray_vappend(dm_args, "-kernel", b_info->kernel, NULL);
+
+        if (b_info->ramdisk)
+            flexarray_vappend(dm_args, "-initrd", b_info->ramdisk, NULL);
+
+        if (b_info->cmdline)
+            flexarray_vappend(dm_args, "-append", b_info->cmdline, NULL);
+
         if (b_info->u.hvm.serial || b_info->u.hvm.serial_list) {
             if ( b_info->u.hvm.serial && b_info->u.hvm.serial_list )
             {