configs: stm32mp15: move bootdelay configuration in defconfig

The STM32MP15 boards have no reason to configure bootdelay in stm32mp1.h
as it is already done with CONFIG_BOOTDELAY (default = 2) and in
include/env_default.h.

This patch allows configuration for customers which reuse stm32mp1.h
and reduce the size of the default environment.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/configs/stm32mp15_basic_defconfig b/configs/stm32mp15_basic_defconfig
index 1c68098..0864d4f 100644
--- a/configs/stm32mp15_basic_defconfig
+++ b/configs/stm32mp15_basic_defconfig
@@ -20,6 +20,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="stm32mp157c-ev1"
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_FIT=y
+CONFIG_BOOTDELAY=1
 CONFIG_BOOTCOMMAND="run bootcmd_stm32mp"
 CONFIG_SPL_LOG=y
 CONFIG_BOARD_EARLY_INIT_F=y