RDMA/mlx5: Rework implicit_mr_get_data

This function is intended to loop across each MTT chunk in the implicit
parent that intersects the range [io_virt, io_virt+bnct).  But it is has a
confusing construction, so:

- Consistently use imr and odp_imr to refer to the implicit parent
  to avoid confusion with the normal mr and odp of the child
- Directly compute the inclusive start/end indexes by shifting. This is
  clearer to understand the intent and avoids any errors from unaligned
  values of addr
- Iterate directly over the range of MTT indexes, do not make a loop
  out of goto
- Follow 'success oriented flow', with goto error unwind
- Directly calculate the range of idx's that need update_xlt
- Ensure that any leaf MR added to the interval tree always results in an
  update to the XLT

Link: https://lore.kernel.org/r/20191009160934.3143-6-jgg@ziepe.ca


Reviewed-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>