arm: ls1021atwr: Add distro secure boot support

Enable validation of boot.scr script prior to its execution dependent
on "secureboot" flag in environment. Disable fall back option to
qspi boot in case of secure boot. Also enable "secureboot=y" flag
in environment for ARM based platforms instead of bootcmd.

Signed-off-by: Sumit Garg <sumit.garg@nxp.com>
Tested-by: Vinitha Pillai <vinitha.pillai@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>
diff --git a/configs/ls1021atwr_nor_SECURE_BOOT_defconfig b/configs/ls1021atwr_nor_SECURE_BOOT_defconfig
index cf99770..c8cb215 100644
--- a/configs/ls1021atwr_nor_SECURE_BOOT_defconfig
+++ b/configs/ls1021atwr_nor_SECURE_BOOT_defconfig
@@ -46,3 +46,4 @@
 # CONFIG_VIDEO_SW_CURSOR is not set
 CONFIG_RSA=y
 CONFIG_SPL_RSA=y
+CONFIG_DISTRO_DEFAULTS=y