net/mlx5: Check vhca_resource_manager capability in each op and add extack msg

Since the follow-up patch is going to remove
mlx5_devlink_port_fn_get_vport() entirely, move the vhca_resource_manager
capability checking to individual ops. Add proper extack message
on the way.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>