apparmor: extend policydb permission set by making use of the xbits

The policydb permission set has left the xbits unused. Make them
available for mediation.

Note: that this does not bring full auditing control of the
permissions as there are not enough bits. The quieting of denials is
provided as that is used more than forced auditing of allowed
permissions.

Signed-off-by: John Johansen <john.johansen@canonical.com>