RDMA: Cleanup undesired pd->uobject usage

Drivers should be using udata to determine if a method is invoked from
user space or kernel space. A pd does not necessarily say a different
objects is kernel or user.

Transforming the tests to use udata eliminates a large number of uobject
references from the drivers.

Signed-off-by: Shamir Rabinovitch <shamir.rabinovitch@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>