mm: slub: update slab_alloc interface to capture slab stacks

Update /sys/kernel/debug/slab/alloc_trace interface to capture
slab stack along with slab object details.

Now output of alloc_trace is:
alloc_list: call_site=mempool_alloc_slab+0x1c/0x28 count=2 object_size=1024
slab_size=1472 slab_name=sgpool-32

mempool_alloc_slab+0x1c/0x28

mempool_init_node+0xdc/0x238

mempool_create+0x58/0x88

sg_pool_init+0x70/0xf8

do_one_initcall+0x15c/0x2e8

kernel_init_freeable+0x334/0x3d8

kernel_init+0x18/0x298

ret_from_fork+0x10/0x18.

Change-Id: I19da702bfd22e5526e2c9a04d22717dc70700ae7
Signed-off-by: Faiyaz Mohammed <faiyazm@codeaurora.org>