net/mlx5: fix ARM build

net/mlx5: fix ARM build

rdma-core v16 has a bug. The following compilation error occurs on ARM
hosts.

In file included
from drivers/net/mlx5/mlx5_glue.h:16:0,
from drivers/net/mlx5/mlx5_glue.c:11:
/usr/include/infiniband/mlx5dv.h:144:2: error: unknown type name 'off_t'
off_t   uar_mmap_offset;
^

As a temporary fix, sys/types.h is included in PMD. This has been fixed in
rdma-core v17. This can be removed when all the Linux distros are shipped
with rdma-core v17 or back-ported fix. As of now, RedHat 7.5 is known to
have rdma-core v16.

Cc: stable@dpdk.org
Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>