verstage: Add debug print when returning from verstage

RETURN_FROM_VERSTAGE is a somewhat tricky construct that we don't
normally do otherwise in coreboot. While it works remarkably well in
general, new development can lead to unintentional interactions with
confusing results. This patch adds a debug print to the verstage right
before returning to the bootblock so that it's obvious this happens,
because otherwise in some cases the last printout in the verstage is
about some TPM commands which can be misleading when execution hangs
after that point.

Signed-off-by: Julius Werner <jwerner@chromium.org>
Change-Id: I9ca68a32d7a50c95d9a6948d35816fee583611bc
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52086
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/security/vboot/verstage.c

@@ -19,6 +19,7 @@ void main(void)
 
 	if (CONFIG(VBOOT_RETURN_FROM_VERSTAGE)) {
 		verstage_main();
+		printk(BIOS_DEBUG, "VBOOT: Returning from verstage.\n");
 	} else {
 		run_romstage();
 		hlt();