This change adds uverbs support for allocation/freeing
of device memory commands.

A new uverbs object is defined of type idr to represent
and track the new resource type allocation per context.

The API requires provider driver to implement 2 new ib_device
callbacks - one for allocation and one for deallocation which
return and accept (respectively) the ib_dm object which represents
the allocated memory on the device.

The support is added via the ioctl command infrastructure
only.
Signed-off-by: NAriel Levkovich <lariel@mellanox.com>
Signed-off-by: NLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>