x86: Enable UPL handoff for SPL

Add the GD_FLG_UPL so that a UPL-handoff is created.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/lib/spl.c b/arch/x86/lib/spl.c
index aad7485..7a03350 100644
--- a/arch/x86/lib/spl.c
+++ b/arch/x86/lib/spl.c
@@ -298,6 +298,9 @@
 	if (IS_ENABLED(CONFIG_QEMU))
 		qemu_chipset_init();
 
+	if (CONFIG_IS_ENABLED(UPL_OUT))
+		gd->flags |= GD_FLG_UPL;
+
 	if (CONFIG_IS_ENABLED(VIDEO)) {
 		struct udevice *dev;
 		int ret;