vbe: Record which phases loaded using VBE

We expect VPL and SPL to load using VBE. Add a record of this so we can
check it in U-Boot proper.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/vbe.h

@@ -25,6 +25,15 @@ enum vbe_phase_t {
 	VBE_PHASE_OS,
 };
 
+/**
+ * struct vbe_handoff - information about VBE progress
+ *
+ * @phases: Indicates which phases used the VBE bootmeth (1 << PHASE_...)
+ */
+struct vbe_handoff {
+	u8 phases;
+};
+
 /**
  * vbe_phase() - get current VBE phase
  *