mempool, trace: use single tracepoint to track memory allocations

Because of #295 (per-CPU tracepoint buffers) some samples may be lost what
quite effectively ruins attempts to track the lifetime of allocations.
Since the ability to show which allocations are still unfreed is not crucial
the simplest solution is be not to use memory_free tracepoints and put all
needed information in memory_malloc_{large, mempool}.

Signed-off-by: Pawel Dziepak <pdziepak@quarnos.org>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>