apparmor: Convert secid mapping to XArrays instead of IDR

apparmor: Convert secid mapping to XArrays instead of IDR

XArrays are a better match than IDR for how AppArmor is mapping
secids.  Specifically AppArmor is trying to keep the allocation
dense. XArrays also have the advantage of avoiding the complexity IDRs
preallocation.

In addition this avoids/fixes a lockdep issue raised in the LKML thread
  "Linux 5.18-rc4"

where there is a report of an interaction between apparmor and IPC,
this warning may have been spurious as the reported issue is in a
per-cpu local lock taken by the IDR. With the one side in the IPC id
allocation and the other in AppArmor's secid allocation.

Description by John Johansen <john.johansen@canonical.com>

Message-Id: <226cee6a-6ca1-b603-db08-8500cd8f77b7@gnuweeb.org>
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: John Johansen <john.johansen@canonical.com>