devlink: Move devlink_info_req struct to be local

As all users of the struct devlink_info_req are already in dev.c, move
this struct from devl_internal.c to be local in dev.c.

Signed-off-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>