Dualcpu: Execute memory access check in privileged level

Some PSA RoT services also require memory access check. Allow
multi-core memory access to be performed not only in Handler mode,
but also in privileged thread mode.

Change-Id: Ic8abec6121a644325b80ac54a0e330460b19eec5
Signed-off-by: David Hu <david.hu@arm.com>