bootblock: Support normal/fallback mechanism again

Change-Id: I7395e62f6682f4ef123da10ac125127a57711ec6
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37760
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/program_loading.h

@@ -179,6 +179,9 @@ struct prog_loader_ops {
 /* Run romstage from bootblock. */
 void run_romstage(void);
 
+/* Runtime selector for CBFS_PREFIX of romstage. */
+int legacy_romstage_selector(struct prog *romstage);
+
 /************************
  *   RAMSTAGE LOADING   *
  ************************/