RDMA/mlx5: Change the cache structure to an RB-tree

Currently, the cache structure is a static linear array. Therefore, his
size is limited to the number of entries in it and is not expandable.  The
entries are dedicated to mkeys of size 2^x and no access_flags. Mkeys with
different properties are not cacheable.

In this patch, we change the cache structure to an RB-tree.  This will
allow to extend the cache to support more entries with different mkey
properties.

Link: https://lore.kernel.org/r/20230125222807.6921-4-michaelgur@nvidia.com
Signed-off-by: Michael Guralnik <michaelgur@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>