net/mlx5: Add sd_group_size bits for SD management

Currently, mlx5 is querying the MPIR register to get the number of PFs
that should comprise the SD group.
However, this register does not reflect the correct number in complex
deployments. Hence, add an sd_group_size field to nic_vport_context to
determine the correct number of PFs, and add an sd_group_size capability
bit to indicate whether FW supports it.

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260529052359.389413-3-tariqt@nvidia.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>