RDMA/mlx5: Add DMAH object support

RDMA/mlx5: Add DMAH object support

This patch introduces support for allocating and deallocating the DMAH
object.

Further details:
----------------
The DMAH API is exposed to upper layers only if the underlying device
supports TPH.

It uses the mlx5_core steering tag (ST) APIs to get a steering tag index
based on the provided input.

The obtained index is stored in the device-specific mlx5_dmah structure
for future use.

Upcoming patches in the series will integrate the allocated DMAH into
the memory region (MR) registration process.

Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Reviewed-by: Edward Srouji <edwards@nvidia.com>
Link: https://patch.msgid.link/778550776799d82edb4d05da249a1cff00160b50.1752752567.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>