Introduce the managing_system privilege for components like the
platform_driver to allow it to call system management functionality
that is reserved by kernel or special firmware, e.g., ARM Trusted Firmware.
The former RAM resource configuration attribute `constrain_phys`,
which enabled to constrain the region of physical RAM to be used,
gets replaced by the new, broader managing_system configuration
attribute of a `start` node. It gets enforced by the sandbox library.
Ref #3816
