powerpc/qspinlock: Add spinlock contention tracepoint

Add a lock contention tracepoint in the queued spinlock slowpath.
Also add the __lockfunc annotation so that in_lock_functions()
works as expected.

Signed-off-by: Nysal Jan K.A. <nysal@linux.ibm.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250731061856.1858898-1-nysal@linux.ibm.com