devlink: remove devlink features

Devlink features were introduced to disallow devlink reload calls of
userspace before the devlink was fully initialized. The reason for this
workaround was the fact that devlink reload was originally called
without devlink instance lock held.

However, with recent changes that converted devlink reload to be
performed under devlink instance lock, this is redundant so remove
devlink features entirely.

Note that mlx5 used this to enable devlink reload conditionally only
when device didn't act as multi port slave. Move the multi port check
into mlx5_devlink_reload_down() callback alongside with the other
checks preventing the device from reload in certain states.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>