arm-bsp-extras: Delegated ATU configuration

RD-Aspen has RSE owning the configuration of all ATUs in the system.
Modify TF-M and SCP-firmware to align with this.

TF-M statically configures the initial ATU configuration and allows
SCP-firmware to make runtime requests for additional translation
regions.

Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>