Add dummy RPC handler for RPCs that are not implemented as control should be returned back to OP-TEE in case any RPC is invoked. Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Sumit Garg <sumit.garg@linaro.org> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>