linux: enable AppArmor-related options if needed

linux: enable AppArmor-related options if needed

Using AppArmor requires support in the kernel, so do for AppArmor what
we did for SElinux, and enabled the necessary options.

Note that a single LSM can be the default one, so as of today, SELinux
wins, by virtue of being the last to be enabled.

Signed-off-by: Angelo Compagnucci <angelo@amarulasolutions.com>
[yann.morin.1998@free.fr:
  - don't force DEFAULT_SECURITY_APPARMOR, it does not exist in all
    kernel versions
  - move closer to SELinux
  - split into its own patch, write a commit log
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Tested-by: Angelo Compagnucci <angelo@amarulasolutions.com>