SECURE_BOOT: Disable IE Key feature for RAMBOOT

SECURE_BOOT: Disable IE Key feature for RAMBOOT

ISBC Key Extension feature is not applicable for RAMBOOT
as there is no way to retrieve the CSF Header and validated
IE Key table from SRAM once CPC has been disabled.
The feature is only applicable in case of NOR SECURE BOOT.
Code Cleanup:
The SECURE_BOOT specific defines have been moved from
arch-ls102xa/config.h to
arm/include/asm/fsl_secure_boot.h

Signed-off-by: Aneesh Bansal <aneesh.bansal@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>