core: prevent allocation when exception index tables are empty
core: prevent allocation when exception index tables are empty

This change prevent the core from allocating memory, mapping and
other resources to map exception index tables that are all empty.

Signed-off-by: Etienne Carriere <f21bc5b8f3ea1962eb45af359f1abea6578cab94@st.com>
Reviewed-by: Jerome Forissier <ced78d268b4c9a0a20a59a9feeebd2ad90da03d3@linaro.org>

pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os