RDMA/uverbs: Use device.groups to initialize device attributes

Instead of explicitly adding device attribute files and handling such
error conditions, depend on device core layer to create device attributes
files based group pointer NULL terminated array.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Daniel Jurgens <danielj@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>