IB/mlx5: Add steering SW ICM device memory type

This patch adds support for allocating, deallocating and registering a new
device memory type, STEERING_SW_ICM.  This memory can be allocated and
used by a privileged user for direct rule insertion and management of the
device's steering tables.

The type is provided by the user via the dedicated attribute in the
alloc_dm ioctl command.

Signed-off-by: Ariel Levkovich <lariel@mellanox.com>
Reviewed-by: Eli Cohen <eli@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>