IB/core: Provide rdma_ versions of the gid cache API

These versions are functionally similar but all return gid_attrs and
related information via reference instead of via copy.

The old API is preserved, implemented as wrappers around the new, until
all callers can be converted.

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