The current implementation of FWU_SMC_IMAGE_RESUME when called
from the normal world, uses the provided image_id argument to
determine which secure image to resume into. This implies that
the normal world has a choice of which secure image to resume
into when in fact it is only possible to resume into the
previously interrupted secure image.

This patch removes the argument, tightens up the pre-conditions
for the SMC and adds additional asserts.

The pre-conditions for FWU_SMC_SEC_IMAGE_DONE are also
tightened up.

Change-Id: Ia5a46753bb01e8f8dad8a2999314f90db8f300e8