RDMA/core: Introduce ib_device_ops

This change introduces the ib_device_ops structure that defines all the
InfiniBand device operations in one place, so the code will be more
readable and clean, unlike today when the ops are mixed with ib_device
data members.

The providers will need to define the supported operations and assign them
using ib_set_device_ops(), that will also make the providers code more
readable and clean.

Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>