RDMA/efa: Use the common mmap_xa helpers

Remove the functions related to managing the mmap_xa database.  This code
was replaced with common code in ib_core.

Link: https://lore.kernel.org/r/20191030094417.16866-5-michal.kalderon@marvell.com


Signed-off-by: Ariel Elior <ariel.elior@marvell.com>
Signed-off-by: Michal Kalderon <michal.kalderon@marvell.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>