IB/mlx5: Device memory support in mlx5_ib

This patch adds the mlx5_ib driver implementation for the device
memory allocation API.
It implements the ib_device callbacks for allocation and deallocation
operations as well as a new mmap command support which allows mapping
an allocated device memory to a VMA.

The change also adds reporting of device memory maximum size and
alignment parameters reported in device capabilities.

The allocation/deallocation operations are using new firmware
commands to allocate MEMIC memory on the device.

Signed-off-by: Ariel Levkovich <lariel@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>