IB/core: Add vendor's specific data to alloc mw

Passing udata to the vendor's driver in order to pass data from the
user-space driver to the kernel-space driver. This data will be
used in downstream patches.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>