configs/rdn1edge: allow support for RAS to be optional

In order to support build of RD-N1-Edge platform with and without
RAS support, add new build defintions ARM_TF_ENABLE_SPM and
ARM_TF_RAS_EXTENSION. These have to be set to '1' in order to
support SPM and RAS support.

Change-Id: I1e4a5d2b9639a23f7e809aff76024222a178d9b0
Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>