RDMA/core: Create the device hw_counters through the normal groups mechanism

Instead of calling device_add_groups() add the group to the existing
groups array which is managed through device_add().

This requires setting up the hw_counters before device_add(), so it gets
split up from the already split port sysfs flow.

Move all the memory freeing to the release function.

Link: https://lore.kernel.org/r/666250d937b64f6fdf45da9e2dc0b6e5e4f7abd8.1623427137.git.leonro@nvidia.com


Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>