devlink: Simplify devlink resources unregister call

The devlink_resources_unregister() used second parameter as an
entry point for the recursive removal of devlink resources. None
of the callers outside of devlink core needed to use this field,
so let's remove it.

As part of this removal, the "struct devlink_resource" was moved
from .h to .c file as it is not possible to use in any place in
the code except devlink.c.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>