arm: stm32mp1: add PSCI support

Add PSCI v1.0 support for Linux and manage PSCI state
for each CPU (affinity 0 level) with all mandatory functions:
- PSCI_VERSION
- CPU_SUSPEND
- CPU_OFF
- CPU_ON
- AFFINITY_INFO
- SYSTEM_OFF
- SYSTEM_RESET
- PSCI_FEATURES
and 1 optional to avoid Linux warning
- MIGRATE_INFO_TYPE

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>