feat(plat/fvp): introduce accessor function to obtain datastore

In order to provide the EL3 SPMC a sufficient datastore to
record memory descriptors, a accessor function is used.
This allows for the backing memory to be allocated in a
platform defined manner, to accommodate memory constraints
and desired use cases.

Provide an implementation for the Arm FVP platform to
use a default value of 512KB memory allocated in the
TZC RAM section.

Signed-off-by: Marc Bonnici <marc.bonnici@arm.com>
Change-Id: I92bc55ba6e04bdad429eb52f0d2960ceda682804
3 files changed