powerpc/mpc85xx: socrates: add autoboot delay string

add autoboot delay string for socrates board.
use sha256 for abort autoboot, use "ao" to abort.

Signed-off-by: Heiko Schocher <hs@denx.de>

configs/socrates_defconfig

@@ -20,6 +20,11 @@ CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_SYS_MONITOR_BASE=0xFFF40000
 CONFIG_BOOTDELAY=1
+CONFIG_AUTOBOOT_KEYED=y
+CONFIG_AUTOBOOT_PROMPT="Enter password to abort autoboot in %d seconds!\n"
+CONFIG_AUTOBOOT_ENCRYPTION=y
+CONFIG_AUTOBOOT_STOP_STR_ENABLE=y
+CONFIG_AUTOBOOT_STOP_STR_SHA256="2dd411308b37266d33c9246821adc5aa4002f0091f5e2aece1953789930ad924"
 CONFIG_BOOT_RETRY=y
 CONFIG_BOOT_RETRY_TIME=120
 CONFIG_RESET_TO_RETRY=y