RDMA/core: Simplify how the port sysfs is created

Use the same technique as gid_attrs now uses to manage the port
sysfs. Bundle everything into three allocations and use a single
sysfs_create_groups() to build everything in one shot.

All the memory is always freed in the kobj release function, removing most
of the error unwinding.

The gid_attr technique and the hw_counters are very similar, merge the two
together and combine the sysfs_create_group() call for hw_counters with
the single sysfs group setup.

Link: https://lore.kernel.org/r/b688f3340694c59f7b44b1bde40e25559ef43cf3.1623427137.git.leonro@nvidia.com


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