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This patch refactors dma request types to remove generic function
pointers from the library. This include modifying the linux_seq
implementation to:
- move the copy/move implementation to the dma ops
- remove one layer of indirection, as the request type no longer need
_data and _ops substructures.

Enforcing dma requests to have a fully qualified generic type, with
function pointers, will cause issues for future kinds of dma
implementation, that might require a different way of handling requests
altogether.

This work is driven by our current work on a parallel dma implementation.

This patch adds the basics for a dma interface, including
type-dependent requests structures, and an API based on explicit
copy/move calls.

The APIs is flexible enough to deal with sync/async calls. The internal
design is inspired by aml_area, with the goal that create/init stay type
specific, but the core interactions are generic.

This is a rewrite of the existing code into a memory library exposing
more of its internal abstractions. This refactoring is required to:
- make progress faster by focusing on the core new features
- abstract more of the underlying components and expose those
abstractions
- build upon existing libraries (memkind) for the internal stuff.

Memkind is used as a crutch here, we do not intend to use it in the long
term, as some of its internal are opposed to what we want (topology
management in particular).

Nevertheless, it currently provides a good allocator internally, and
decent access to deep memory, for now.

Over time, we figured out that the best way to build this API was to
create several layers of APIs, each with more abstractions over the
devices. At the same time, we want each layer to expose its internal
mechanisms, so that a user can customize any of them.

This is why we end up with areas and dma engines, and we will add in the
future other stuff, like data decomposition and distribution methods, as
well as direct support for "pipelining".