Docs: Update LSM/apparmor.rst

After the deprecation of CONFIG_DEFAULT_SECURITY, it is no longer used
to enable and configure AppArmor. Since kernel 5.0,
`CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE` is not used either.
Instead, the CONFIG_LSM parameter manages the order and selection of LSMs.

Signed-off-by: Siddharth Menon <simeddon@gmail.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

Documentation/admin-guide/LSM/apparmor.rst

@@ -18,8 +18,11 @@ set ``CONFIG_SECURITY_APPARMOR=y``
 
 If AppArmor should be selected as the default security module then set::
 
-   CONFIG_DEFAULT_SECURITY="apparmor"
-   CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE=1
+   CONFIG_DEFAULT_SECURITY_APPARMOR=y
+
+The CONFIG_LSM parameter manages the order and selection of LSMs.
+Specify apparmor as the first "major" module (e.g. AppArmor, SELinux, Smack)
+in the list.
 
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