maple_tree: Be more strict about locking

Use lockdep to check the write path in the maple tree holds the lock in
write mode.

Introduce mt_write_lock_is_held() to check if the lock is held for
writing.  Update the necessary checks for rcu_dereference_protected() to
use the new write lock check.

Link: https://lkml.kernel.org/r/20230714195551.894800-5-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oliver Sang <oliver.sang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>