flask: change default state to enforcing

flask: change default state to enforcing

The previous default of "permissive" is meant for developing or
debugging a disaggregated system.  However, this default makes it too
easy to accidentally boot a machine in this state, which does not place
any restrictions on guests.  This is not suitable for normal systems
because any guest can perform any operation (including operations like
rebooting the machine, kexec, and reading or writing another domain's
memory).

This change will cause the boot to fail if you do not specify an XSM
policy during boot; if you need to load a policy from dom0, use the
"flask=late" boot parameter.

Original patch by Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; modified
to also change the default value of flask_enforcing so that the policy
is not still in permissive mode.  This also removes the (no longer
documented) command line argument directly changing that variable since
it has been superseded by the flask= parameter.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>