RDMA/mlx5: Add support in MEMIC operations

MEMIC buffer, in addition to regular read and write operations, can
support atomic operations from the host.

Introduce and implement new UAPI to allocate address space for MEMIC
operations such as atomic. This includes:

1. Expose new IOCTL for request mapping of MEMIC operation.
2. Hold the operations address in a list, so same operation to same DM
   will be allocated only once.
3. Manage refcount on the mlx5_ib_dm object, so it would be keep valid
   until all addresses were unmapped.

Link: https://lore.kernel.org/r/20210411122924.60230-7-leon@kernel.org
Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>