SCMI shared memory is used to exchange message payloads between
secure SCMI services and non-secure SCMI agents. It is mapped
uncached (device) mainly to conform to existing support in
the Linux kernel. Note that executive messages are mostly short
(few 32bit words) hence not using cache will not penalize much
performances.

Platform stm32mp1 shall configure ETZPC to harden properly the
secure and non-secure areas of the SYSRAM address space, that before
CPU accesses the shared memory when mapped non-secure.

This change defines STM32MP_SEC_SYSRAM_BASE/STM32MP_SEC_SYSRAM_SIZE and
STM32MP_NS_SYSRAM_BASE/STM32MP_NS_SYSRAM_SIZE.

Change-Id: I71ff02a359b9668ae1c5a71b5f102cf3d310f289
Signed-off-by: Etienne Carriere <etienne.carriere@st.com>