net/mlx5: DR, Expose steering domain functionality

Domain is the frame for all of the dr (direct rule) objects.
There are different domain types which also affect the object under that
domain. Each domain can hold multiple tables which can hold multiple
matchers and so on, this means that all of the dr (direct rule) objects
exist under a specific domain. The domain object also holds the
resources needed for other objects such as memory management and
communication with the device.

Signed-off-by: Alex Vesker <valex@mellanox.com>
Reviewed-by: Erez Shitrit <erezsh@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>