Rather that a CPU reset, tamper must call the system
reset to restart from a clean environment.

Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Change-Id: I5c5482e4473078283783ad04f202c70b561b27ee
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/186543


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: Yann GAUTIER <yann.gautier@st.com>