xsm: create idle domain privileged and demote after setup

xsm: create idle domain privileged and demote after setup

There are new capabilities, dom0less and hyperlaunch, that introduce internal
hypervisor logic, which needs to make resource allocation calls that are
protected by XSM access checks. The need for these resource allocations are
necessary for dom0less and hyperlaunch when they are constructing the initial
domain(s).  This creates an issue as a subset of the hypervisor code is
executed under a system domain, the idle domain, that is represented by a
per-CPU non-privileged struct domain. To enable these new capabilities to
function correctly but in a controlled manner, this commit changes the idle
system domain to be created as a privileged domain under the default policy and
demoted before transitioning to running. A new XSM hook,
xsm_set_system_active(), is introduced to allow each XSM policy type to demote
the idle domain appropriately for that policy type. In the case of SILO, it
inherits the default policy's hook for xsm_set_system_active().

For flask, a stub is added to ensure that flask policy system will function
correctly with this patch until flask is extended with support for starting the
idle domain privileged and properly demoting it on the call to
xsm_set_system_active().

Signed-off-by: Daniel P. Smith <dpsmith@apertussolutions.com>
Reviewed-by: Jason Andryuk <jandryuk@gmail.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Acked-by: Julien Grall <jgrall@amazon.com> # arm
Reviewed-by: Rahul Singh <rahul.singh@arm.com>
Tested-by: Rahul Singh <rahul.singh@arm.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>