refactor(arm)!: rename PLAT_MHU_VERSION flag

In order to support a platform without MHU in RSE, update the flag
PLAT_MHU_VERSION. It is renamed PLAT_MHU and can take the following
entries: NO_MHU, MHUv1, MHUv2, MHUv3...

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: Ia72e590088ce62ba8c9009f341b6135926947bee
4 files changed