RDMA/mlx5: Implement mkeys management via LIFO queue

RDMA/mlx5: Implement mkeys management via LIFO queue

Currently, mkeys are managed via xarray. This implementation leads to
a degradation in cases many MRs are unregistered in parallel, due to xarray
internal implementation, for example: deregistration 1M MRs via 64 threads
is taking ~15% more time[1].

Hence, implement mkeys management via LIFO queue, which solved the
degradation.

[1]
2.8us in kernel v5.19 compare to 3.2us in kernel v6.4

Signed-off-by: Shay Drory <shayd@nvidia.com>
Link: https://lore.kernel.org/r/fde3d4cfab0f32f0ccb231cd113298256e1502c5.1695283384.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>