debugobjects: Rework object freeing

__free_object() is uncomprehensibly complex. The same can be achieved by:

   1) Adding the object to the per CPU pool

   2) If that pool is full, move a batch of objects into the global pool
      or if the global pool is full into the to free pool

This also prepares for batch processing.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/all/20241007164913.955542307@linutronix.de