fix(drtm): return proper values for DRTM get and set error SMCs

The DRTM get and set error previously returned SMC_UNK when these
SMCs were issued. This has been corrected to return an appropriate
error code on failure, and success otherwise.
Also,align the error code values with the specification.

Change-Id: I8f11f94f1ab097245003dbde97365fa54e0097ba
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
2 files changed