plat-stm: add a default test support for SDP
plat-stm: add a default test support for SDP

If SDP is enabled and no SDP memory is defined, a default SDP memory
area of 3Mbyte is defined between the TA_RAM and the NS_SHM. This
change allows to ease test of the SDP feature on the ST platforms.

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