net/mlx5e: Remove unused mlx5e_dcbnl_build_rep_netdev function

Commit
7a9fb35e8c3a ("net/mlx5e: Do not reload ethernet ports when changing eswitch mode")
removed the usage of mlx5e_dcbnl_build_rep_netdev() from the driver,
delete the function.

Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

net/mlx5e: Fix port buffers cell size value

Device unit for port buffers size, xoff_threshold and xon_threshold is
cells. Fix a bug in driver where cell unit size was hard-coded to
128 bytes. This hard-coded value is buggy, as it is wrong for some hardware
versions.

Driver to read cell size from SBCAM register and translate bytes to cell
units accordingly.

In order to fix the bug, this patch exposes SBCAM (Shared buffer
capabilities mask) layout and defines.

If SBCAM.cap_cell_size is valid, use it for all bytes to cells
calculations. If not valid, fallback to 128.

Cell size do not change on the fly per device. Instead of issuing SBCAM
access reg command every time such translation is needed, cache it in
mlx5e_dcbx as part of mlx5e_dcbnl_initialize(). Pass dcbx.port_buff_cell_sz
as a param to every function that needs bytes to cells translation.

While fixing the bug, move MLX5E_BUFFER_CELL_SHIFT macro to
en_dcbnl.c, as it is only used by that file.

Fixes: 0696d60853d5 ("net/mlx5e: Receive buffer configuration")
Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Reviewed-by: Huy Nguyen <huyn@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

net/mlx5e: Take DCBNL-related definitions into dedicated files

Take DCBNL-related definitions out of the common en.h header,
Use a dedicated header file for exposing them.
Some need not to be exposed, use them locally in the .c file.
Use stubs to eliminate use of CONFIG_MLX5_CORE_EN_DCB in the
generic control flows.

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>