RDMA: Change ops->init_port to ops->port_groups

RDMA: Change ops->init_port to ops->port_groups

init_port was only being used to register sysfs attributes against the
port kobject. Now that all users are creating static attribute_group's we
can simply set the attribute_group list in the ops and the core code can
just handle it directly.

This makes all the sysfs management quite straightforward and prevents any
driver from abusing the naked port kobject in future because no driver
code can access it.

Link: https://lore.kernel.org/r/114f68f3d921460eafe14cea5a80ca65d81729c3.1623427137.git.leonro@nvidia.com
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>