net: devlink: clean-up empty devlink_ops::info_get()

devlink_ops::info_get() is now optional and devlink will continue to
report information even if that callback gets removed.

Remove all the empty devlink_ops::info_get() callbacks from the
drivers.

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>