configs: sandbox_defconfig: enable stage pre-load in bootm

Enable the support of stage pre-load in bootm.
For the moment, this stage allow to verify the
signature of the full image with a header.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 0f43101..2c9b37a 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -27,6 +27,8 @@
 CONFIG_AUTOBOOT_NEVER_TIMEOUT=y
 CONFIG_AUTOBOOT_STOP_STR_ENABLE=y
 CONFIG_AUTOBOOT_STOP_STR_CRYPT="$5$rounds=640000$HrpE65IkB8CM5nCL$BKT3QdF98Bo8fJpTr9tjZLZQyzqPASBY20xuK5Rent9"
+CONFIG_IMAGE_PRE_LOAD=y
+CONFIG_IMAGE_PRE_LOAD_SIG=y
 CONFIG_CONSOLE_RECORD=y
 CONFIG_CONSOLE_RECORD_OUT_SIZE=0x1000
 CONFIG_PRE_CONSOLE_BUFFER=y
@@ -36,6 +38,7 @@
 CONFIG_ANDROID_AB=y
 CONFIG_CMD_CPU=y
 CONFIG_CMD_LICENSE=y
+CONFIG_CMD_BOOTM_PRE_LOAD=y
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_BOOTEFI_HELLO=y
 CONFIG_CMD_ABOOTIMG=y