Consider CONFIG_ZERO_BOOTDELAY_CHECK when CONFIG_AUTOBOOT_KEYED is set

When CONFIG_ZERO_BOOTDELAY_CHECK is not defined, bootdelay==0
prevents the check for console input (as stated in README.autoboot).
This must also work in CONFIG_AUTOBOOT_KEYED mode.

Signed-off-by: Dirk Eibach <eibach@gdsys.de>