Shared RAM region in the remote chip's memory is used as one of the
mailbox region (SCMI payload area) through which the AP core on the
local chip and SCP core on the remote chip exchange SCMI protocol
message during the initialization. Mark this region as non-cacheable in
the MMAP entry to prevent local AP core from reading stale data from the
cache.

Change-Id: I7e9dc5fbcc3b40e9bcff5499f15abd2aadaed385
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>