IB/core: Add umem function to read data from user-space

In some drivers there's a need to read data from a user space area
that was pinned using ib_umem when running from a different process
context.

The ib_umem_copy_from function allows reading data from the physical
pages pinned in the ib_umem struct.

Signed-off-by: Haggai Eran <haggaie@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

diff --cc drivers/infiniband/core/umem.c
Simple merge

diff --cc include/rdma/ib_umem.h
Simple merge