This patch supports driver APIs "add_sub_dev" and "del_sub_dev", to
add and delete a plane device respectively.
A mlx5 plane device is a rdma SMI device; It provides the SMI capability
through user MAD for it's parent, the logical multi-plane aggregated
device. For a plane port:
- It supports QP0 only;
- When adding a plane device, all plane ports are added;
- For some commands like mad_ifc, both plane_index and native portnum
  is needed;
- When querying or modifying a plane port context, the native portnum
  must be used, as the query/modify_hca_vport_context command doesn't
  support plane port.
Signed-off-by: Mark Zhang <markzhang@nvidia.com>
Link: https://lore.kernel.org/r/e933cd0562aece181f8657af2ca0f5b387d0f14e.1718553901.git.leon@kernel.orgSigned-off-by: Leon Romanovsky <leonro@nvidia.com>