mm: slub: Declare slab_owner_ops only when SLUB DEBUG is enabled

Declare the ops struct and corresponding callbacks only when
SLUB_DEBUG is enabled.
Currently, the ops is defined only under
MINIDUMP_PANIC_DUMP config but the variables it uses are protected
under SLUB_DEBUG as well.

Change-Id: I11f29564e1d65edc506a50e2c12aac374dbca6d5
Signed-off-by: Rohit Agarwal <quic_rohiagar@quicinc.com>