RDMA/mlx5: Replace ent->lock with xa_lock

In the next patch, ent->list will be replaced with an xarray. The xarray
uses an internal lock to protect the indexes. Use it to protect all the
entry fields, and get rid of ent->lock.

Link: https://lore.kernel.org/r/20220726071911.122765-2-michaelgur@nvidia.com


Signed-off-by: Aharon Landau <aharonl@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>