autoboot: remove CONFIG_ZERO_BOOTDELAY_CHECK

As the help message of CONFIG_BOOTDELAY says, CONFIG_BOOTDELAY=-2
means the autoboot with no delay, with no abort check even if
CONFIG_ZERO_BOOTDELAY_CHECK is defined.

To sum up, the autoboot behaves as follows:

 [1] CONFIG_BOOTDELAY=0 && CONFIG_ZERO_BOOTDELAY_CHECK=y
    autoboot with no delay, but you can abort it by key input

 [2] CONFIG_BOOTDELAY=0 && CONFIG_ZERO_BOOTDELAY_CHECK=n
    autoboot with no delay, with no check for abort

 [3] CONFIG_BOOTDELAY=-1
    disable autoboot

 [4] CONFIG_BOOTDELAY=-2
    autoboot with no delay, with no check for abort

As you notice, [2] and [4] come to the same result, which means we
do not need CONFIG_ZERO_BOOTDELAY_CHECK.  We can control all the
cases only by CONFIG_BOOTDELAY, like this:

 [1] CONFIG_BOOTDELAY=0
    autoboot with no delay, but you can abort it by key input

 [2] CONFIG_BOOTDELAY=-1
    disable autoboot

 [3] CONFIG_BOOTDELAY=-2
    autoboot with no delay, with no check for abort

This commit converts the logic as follow:
  CONFIG_BOOTDELAY=0 && CONFIG_ZERO_BOOTDELAY_CHECK=n
    --> CONFIG_BOOTDELAY=-2

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Vladimir Zapolskiy <vz@mleia.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Acked-by: Christian Riesch <christian.riesch@omicronenergy.com>
Acked-by: Hannes Schmelzer <hannes.schmelzer@br-automation.com>
diff --git a/configs/brppt1_nand_defconfig b/configs/brppt1_nand_defconfig
index 85ddbe7..a14a130 100644
--- a/configs/brppt1_nand_defconfig
+++ b/configs/brppt1_nand_defconfig
@@ -3,7 +3,7 @@
 CONFIG_SPL=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_SYS_EXTRA_OPTIONS="SERIAL1,CONS_INDEX=1,NAND"
-CONFIG_BOOTDELAY=0
+CONFIG_BOOTDELAY=-2
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set