RDMA/core: Move device addition deletion to device.c

Move core device addition and removal from sysfs.c to device.c as device.c
is more appropriate place for device management.

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